cmd/tailscale/cli: don't run CLI as a service on gokrazy

Updates #13038
Updates #1866

Change-Id: Ie3223573044a92f5715a827fb66cc6705b38004f
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f