These accidentally make the tag syntax more flexible than was intended,
which will create forward compatibility problems later. Let's go back
to the old stricter parser.
Revert "cmd/tailscale/cli: fix double tag: prefix in tailscale up"
Revert "cmd/tailscale/cli, tailcfg: allow tag without "tag:" prefix in 'tailscale up'"
This reverts commit a702921620f7b6e386f393a9a1340d4218597469.
This reverts commit cd07437ade.
Affects #861.
Signed-off-by: Avery Pennarun <apenwarr@tailscale.com>
f99f6608ff