These were a mistake, they make the type signatures harder to read and
less flexible. The CommandSeek, CommandStart, CommandPerform, and
CommandCleanup types were a good idea, but composing them with the
parameters expected is going too far.
Do not set annex.version whenever any command is run. Just do it in init.
This ensures that, if a repo has annex.version=3, it has a git-annex
branch, so we don't have to run a command every time to check for the
branch.
Remove the old ad-hoc logic for v0 and v1, to simplify version checking.
