feature/taildrop, ipn/ipnlocal: remove leftover dup calls to osshare

I'd moved the osshare calls to feature/taildrop hooks, but forgot to
remove them from ipnlocal, or lost them during a rebase.

But then I noticed cmd/tailscaled also had some, so turn those into a
hook.

Updates #12614

Change-Id: I024fb1d27fbcc49c013158882ee5982c2737037d
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscaled/depaware.txt

@@ -253,6 +253,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/clientupdate                                   from tailscale.com/client/web+
   LW    tailscale.com/clientupdate/distsign                          from tailscale.com/clientupdate
         tailscale.com/cmd/tailscaled/childproc                       from tailscale.com/cmd/tailscaled+
+        tailscale.com/cmd/tailscaled/tailscaledhooks                 from tailscale.com/cmd/tailscaled+
         tailscale.com/control/controlbase                            from tailscale.com/control/controlhttp+
         tailscale.com/control/controlclient                          from tailscale.com/cmd/tailscaled+
         tailscale.com/control/controlhttp                            from tailscale.com/control/controlclient