tests/narrow-library.sh

repo: remove now-unused changectx() method (API)

repo.changectx(x) was just a synonym for repo[x], so any extensions
that fail due to this commit should switch over to that form.

Differential Revision: https://phab.mercurial-scm.org/D3037

cat >> $HGRCPATH <<EOF
[extensions]
narrow=
[ui]
ssh=python "$TESTDIR/dummyssh"
[experimental]
changegroup3 = True
EOF