[infra] Patch submitters can remove core reviewer votes?

See https://review.openstack.org/#/c/637703/

I'm assuming in that case it was an accident, but it doesn't seem like this should be possible at all. For example, if I had -2'd would it still have allowed the removal? Maybe you can only remove positive votes?

Anyway, seemed weird to me so I thought I would bring it up.

-Ben