changegroup: don't use 'repo' for non-repo 'self'
'repo' is a very confusing name to use for 'self', especially when
it's not a repo. Also drop repo.ui member (a.k.a. self.ui) now that
'self' doesn't shadow outer 'repo' variable.
Testing that hghave does not crash when checking features $ hghave --test-features 2>/dev/null