test: enable sparse-revlog for test-remotefilelog-clone.t
We are about to enable sparse-revlog globally. To help with reviewing the
tests change, we isolate them in individual changesets.
Differential Revision: https://phab.mercurial-scm.org/D5329
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.