Prevent plugin developers from removing their own commit access, if they're the only account

[Ipstenu]

If a plugin only has one person with commit access, we should NOT allow that person to remove their own commit bit.

We should require they add someone before they can remove themselves. That way we can prevent silly moments where a dev clicked the wrong thing.

Note: ADMINS should remain able to remove all committers as we sometimes need to do this for security.

[dd32]

In 7876:

Plugin Directory: Prevent a user removing themselves as the committer, if they're the only committer.

Fixes #3923.

[dd32]

[7876] covers the scenario here, where there's only one user.

If there's multiple committers, one can revoke their own commit still, which then also locks them out of being able to delete any other committers - so it's impossible for a non-admin to ever end up with no committers on a plugin.

[Ipstenu]

That's fine if they remove themselves, as long as there's ONE committer :)