util/eventbus: remove debug UI from iOS build

The use of html/template causes reflect-based linker bloat. Longer
term we have options to bring the UI back to iOS, but for now, cut
it out.

Updates #15297

Signed-off-by: David Anderson <dave@tailscale.com>

util/eventbus/debughttp.go

@@ -1,6 +1,8 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
+//go:build !ios
+
 package eventbus
 
 import (