refs: refactor resolve_gitlink_ref() to accept a repository

In `resolve_gitlink_ref()` we implicitly rely on `the_repository` to
look up the submodule ref store. Now that we can look up submodule ref
stores for arbitrary repositories we can improve this function to
instead accept a repository as parameter for which we want to resolve
the gitlink.

Do so and adjust callers accordingly.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff-lib.c

@@ -66,7 +66,8 @@ static int check_removed(const struct cache_entry *ce, struct stat *st)
 		 * a directory --- the blob was removed!
 		 */
 		if (!S_ISGITLINK(ce->ce_mode) &&
-		    resolve_gitlink_ref(ce->name, "HEAD", &sub))
+		    repo_resolve_gitlink_ref(the_repository, ce->name,
+					     "HEAD", &sub))
 			return 1;
 	}
 	return 0;