[CQ] remove (stale) deploy plugin command

[pq]

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read the Flutter Style Guide recently, and have followed its advice.
• I signed the CLA.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[jwren]

Thanks Phil!