wireproto: disallow commands handlers for multiple transport versions
I think it will be more trouble than it is worth to code version 1
and version 2 command handlers to the same interface. It will feel
awkward to shoehorn functionality into e.g. the version 1 protocol
handler interface. This would likely constrain the ability for version
2 to evolve.
Previous commits introduced a clean separation between command handlers
for version 1 and version 2 transports. This commit reinforces that
separation by dropping support for having a single command handler
service both version 1 and version 2 transports.
Differential Revision: https://phab.mercurial-scm.org/D3208
(binary:application/octet-stream)