cmd/relaynode: drop local --acl-file in favour of central packet filter.

relaynode itself is not long for this world, deprecated in favour of
tailscale/tailscaled. But now that the control server supports central
distribution of packet filters, let's actually take advantage of it in
a final, backward compatible release of relaynode.

.gitignore

@@ -1,6 +1,6 @@
 # Binaries for programs and plugins
+*~
 *.exe
-*.exe~
 *.dll
 *.so
 *.dylib