Revert "cmd/tailscale/cli: disallow --ssh on Synology"

This reverts commit 03e3e6abcd
in favor of #4785.

Change-Id: Ied65914106917c4cb8d15d6ad5e093a6299d1d48
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