ipn/ipnlocal, wgengine/wgcfg/nmcfg: stop building peer lists on delta path

Processing a peer add/remove delta still materialized the full netmap
(an O(n) slicesx.MapValues plus sort over all peers, at 10k+
peers in a large tailnet) twice per delta: once in UpdateNetmapDelta
purely to hand the self node to Engine.SetSelfNode, and once in
authReconfigLocked.

Neither needs peers anymore. SetSelfNode gets the self node from the
existing nodeBackend.Self accessor. authReconfigLocked only reads
self-node fields (SelfNode, NodeKey, GetAddresses, HasCap) now that
WireGuard peers ride the incremental route manager and per-peer config
source, so it can use the peers-free NetMap accessor.

That also makes nmcfg.WGCfg vestigial: since wgcfg.Config lost its
Peers field, its peer walk existed only to emit the [v1] skip logs
(expired peers, unselected exit nodes, unaccepted subnet routes),
duplicating filtering the route manager already does. Delete the
package and construct the two-field wgcfg.Config inline. The skip
logs go away; if they're missed, the route manager can log them
incrementally at upsert time instead of rescanning every peer on
every reconfig.

With this, the runtime.DidRange analysis (see the ts_rangehook test)
shows a delta netmap update performing no O(n) range loops except
updateRouteManagerExtras, and the delta phase of that test drops from
1.09s to 0.14s for 400 deltas at n=10000 (from 4.79s at the
start of this effort, before the incremental route manager work).

Updates #12542

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: Ia0e03ef9db0c988790b2c29de1f0505305e93f58

cmd/k8s-operator/depaware.txt

@@ -928,7 +928,6 @@ tailscale.com/cmd/k8s-operator dependencies: (generated by github.com/tailscale/
         tailscale.com/wgengine/netstack/gro                          from tailscale.com/net/tstun+
         tailscale.com/wgengine/router                                from tailscale.com/ipn/ipnlocal+
         tailscale.com/wgengine/wgcfg                                 from tailscale.com/ipn/ipnlocal+
-        tailscale.com/wgengine/wgcfg/nmcfg                           from tailscale.com/ipn/ipnlocal
      💣 tailscale.com/wgengine/wgint                                 from tailscale.com/wgengine+
         tailscale.com/wgengine/wglog                                 from tailscale.com/wgengine
         golang.org/x/crypto/argon2                                   from tailscale.com/tka

cmd/tailscaled/depaware-min.txt

@@ -200,7 +200,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/wgengine/netstack/gro                          from tailscale.com/net/tstun+
         tailscale.com/wgengine/router                                from tailscale.com/cmd/tailscaled+
         tailscale.com/wgengine/wgcfg                                 from tailscale.com/ipn/ipnlocal+
-        tailscale.com/wgengine/wgcfg/nmcfg                           from tailscale.com/ipn/ipnlocal
      💣 tailscale.com/wgengine/wgint                                 from tailscale.com/wgengine+
         tailscale.com/wgengine/wglog                                 from tailscale.com/wgengine
         golang.org/x/crypto/blake2b                                  from golang.org/x/crypto/nacl/box

cmd/tailscaled/depaware-minbox.txt

@@ -221,7 +221,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/wgengine/netstack/gro                          from tailscale.com/net/tstun+
         tailscale.com/wgengine/router                                from tailscale.com/cmd/tailscaled+
         tailscale.com/wgengine/wgcfg                                 from tailscale.com/ipn/ipnlocal+
-        tailscale.com/wgengine/wgcfg/nmcfg                           from tailscale.com/ipn/ipnlocal
      💣 tailscale.com/wgengine/wgint                                 from tailscale.com/wgengine+
         tailscale.com/wgengine/wglog                                 from tailscale.com/wgengine
         golang.org/x/crypto/blake2b                                  from golang.org/x/crypto/nacl/box

cmd/tailscaled/depaware.txt

@@ -521,7 +521,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/wgengine/router                                from tailscale.com/cmd/tailscaled+
         tailscale.com/wgengine/router/osrouter                       from tailscale.com/feature/condregister
         tailscale.com/wgengine/wgcfg                                 from tailscale.com/ipn/ipnlocal+
-        tailscale.com/wgengine/wgcfg/nmcfg                           from tailscale.com/ipn/ipnlocal
      💣 tailscale.com/wgengine/wgint                                 from tailscale.com/wgengine+
         tailscale.com/wgengine/wglog                                 from tailscale.com/wgengine
    W 💣 tailscale.com/wgengine/winnet                                from tailscale.com/wgengine/router/osrouter

cmd/tsidp/depaware.txt

@@ -326,7 +326,6 @@ tailscale.com/cmd/tsidp dependencies: (generated by github.com/tailscale/depawar
         tailscale.com/wgengine/netstack/gro                          from tailscale.com/net/tstun+
         tailscale.com/wgengine/router                                from tailscale.com/ipn/ipnlocal+
         tailscale.com/wgengine/wgcfg                                 from tailscale.com/ipn/ipnlocal+
-        tailscale.com/wgengine/wgcfg/nmcfg                           from tailscale.com/ipn/ipnlocal
      💣 tailscale.com/wgengine/wgint                                 from tailscale.com/wgengine+
         tailscale.com/wgengine/wglog                                 from tailscale.com/wgengine
         golang.org/x/crypto/argon2                                   from tailscale.com/tka