net/dnsfallback: remove net/dnsfallback go:generate line

We should be able to freely run `./tool/go generate ./...`, but we're
continually dodging this particular generator. Instead of constantly
dodging it, let's just remove it.

Updates #cleanup
Signed-off-by: James Tucker <james@tailscale.com>

net/dnsfallback/dnsfallback.go

@@ -1,10 +1,13 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
-//go:generate go run update-dns-fallbacks.go
-
 // Package dnsfallback contains a DNS fallback mechanism
 // for starting up Tailscale when the system DNS is broken or otherwise unavailable.
+//
+// The data is backed by a JSON file `dns-fallback-servers.json` that is updated
+// by `update-dns-fallbacks.go`:
+//
+//	(cd net/dnsfallback; go run update-dns-fallbacks.go)
 package dnsfallback
 
 import (