changegroup: remove _clnodetorev
cgpacker._clnodetorev is a glorified cache/index of changelog
nodes to revision numbers.
I'm not sure why it exists. Maybe performance? But its presence
is making refactoring of this code more complicated than it needs
to be.
This commit removes the cache and replaces it with direct lookups
against the changelog.
If this cache was for performance reasons, we should be able to
restore it easily enough... after the changegroup refactor is
complete.
Differential Revision: https://phab.mercurial-scm.org/D4189
#require docutils gettext
$ $TESTDIR/check-gendoc el
checking for parse errors