tests: don't load strip extension via mq extension for remotefilelog tests

The proper way to get the `hg strip` command has been via the "strip"
extension since 2013.

Differential Revision: https://phab.mercurial-scm.org/D5250

tests/remotefilelog-library.sh

@@ -6,7 +6,7 b' debug=True'
 [extensions]
 remotefilelog=
 rebase=
-mq=
+strip=
 [ui]
 ssh=python "$TESTDIR/dummyssh"
 [server]