revisions API users: add straightforward release_revisions()

Add a release_revisions() to various users of "struct rev_list" in
those straightforward cases where we only need to add the
release_revisions() call to the end of a block, and don't need to
e.g. refactor anything to use a "goto cleanup" pattern.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ref-filter.c

@@ -2392,6 +2392,7 @@ static void reach_filter(struct ref_array *array,
 		clear_commit_marks(merge_commit, ALL_REV_FLAGS);
 	}
 
+	release_revisions(&revs);
 	free(to_clear);
 }