tests: drop extra "file:" prefix from paths in narrow test
It looks like these were added by mistake in f4d4bd8c8911 (narrow: add
a --narrowspec flag to clone command, 2018-08-08).
Differential Revision: https://phab.mercurial-scm.org/D4531
#require docutils gettext $ $TESTDIR/check-gendoc da checking for parse errors