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>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f