wireprotov2: remove functions for creating response frames from bytes
All code in the actual server uses oncommandresponsereadyobjects().
Test code was ported to that method. This resulted in a handful of
subtle test changes.
Differential Revision: https://phab.mercurial-scm.org/D4924
cat >> $HGRCPATH <<EOF
[extensions]
narrow=
[ui]
ssh=python "$TESTDIR/dummyssh"
[experimental]
changegroup3 = True
EOF