tests/narrow-library.sh

copies: delete now-unnecessary check for "a == b" before "a.descendant(b)"

Unnecessary since 879cbdde63df (revlog: do inclusive descendant
testing (API), 2018-06-21).

Differential Revision: https://phab.mercurial-scm.org/D3935

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