Another baby step toward removing slices of peers from the engine. getStatus iterated peerSequence (a key snapshot built in Reconfig from cfg.Peers) and then asked wgdev for each peer's stats; peers that weren't active in wgdev silently fell out. Iterate active wgdev peers directly via RemoveMatchingPeers(returnFalse) instead. Updates #12542 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com> Change-Id: I3abd348abc30db706db29b3a785179259e48abda