metadump: fix cleanup for v1 metadump testing

metadump: fix cleanup for v1 metadump testing

In commit ce79de11337e38, the metadump v2 tests were updated to leave
the names of loop devices in some global variables so that the cleanup
method can find them and remove the loop devices.  Inexplicably, the
metadump v1 test function was not upgraded.  Do so now.

Cc: <fstests@vger.kernel.org> # v2024.12.08
Fixes: ce79de11337e38 ("fstests: clean up loop device instantiation")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>