ipn/localapi: dead code eliminate unreachable/useless LocalAPI handlers when disabled

Saves ~94 KB from the min build.

Updates #12614

Change-Id: I3b0b8a47f80b9fd3b1038c2834b60afa55bf02c2
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/local.go

@@ -4621,7 +4621,7 @@ func (b *LocalBackend) setPrefsLockedOnEntry(newp *ipn.Prefs, unlock unlockOnce)
 
 	b.updateFilterLocked(newp.View())
 
-	if oldp.ShouldSSHBeRunning() && !newp.ShouldSSHBeRunning() {
+	if buildfeatures.HasSSH && oldp.ShouldSSHBeRunning() && !newp.ShouldSSHBeRunning() {
 		if b.sshServer != nil {
 			b.goTracker.Go(b.sshServer.Shutdown)
 			b.sshServer = nil
@@ -5917,6 +5917,9 @@ func (b *LocalBackend) setWebClientAtomicBoolLocked(nm *netmap.NetworkMap) {
 //
 // b.mu must be held.
 func (b *LocalBackend) setExposeRemoteWebClientAtomicBoolLocked(prefs ipn.PrefsView) {
+	if !buildfeatures.HasWebClient {
+		return
+	}
 	shouldExpose := prefs.Valid() && prefs.RunWebClient()
 	b.exposeRemoteWebClientAtomicBool.Store(shouldExpose)
 }