Add a test for unblocking, then removing, a contact.
Add a test for unblocking, then removing, a contact.

Unblocking is actually not tested anywhere, so this serves as a simple
smoke-test for that, as well as testing that unblock followed by
remove-from-stored works when the latter is queued.

community-ssu/telepathy-gabble,community-ssu/telepathy-gabble,community-ssu/telepathy-gabble,community-ssu/telepathy-gabble