Remove `sendMessage` and `q2q-message` protocol.

There was only code for the sending side, and this would make more sense to live separately from `Q2QService`.
Merge pull request #11 from twisted/remove-q2q-message-protocol

Remove `sendMessage` and `q2q-message` protocol.

Reviewer: cyli

There was only code for the sending side, and this would make more sense to live separately from Q2QService.
Fixes #10