files-backend: drop refs parameter from split_symref_update()

This parameter was added in fcc42ea0c9 (split_symref_update(): add a
files_ref_store argument, 2016-09-04) without comment, but never used.
The splitting is purely mechanical, and doesn't depend on the particular
ref-store. Let's drop this parameter in the name of simplicity.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs/files-backend.c

@@ -2254,8 +2254,7 @@ static int split_head_update(struct ref_update *update,
  * Note that the new update will itself be subject to splitting when
  * the iteration gets to it.
  */
-static int split_symref_update(struct files_ref_store *refs,
-			       struct ref_update *update,
+static int split_symref_update(struct ref_update *update,
 			       const char *referent,
 			       struct ref_transaction *transaction,
 			       struct string_list *affected_refnames,
@@ -2449,7 +2448,7 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 			 * of processing the split-off update, so we
 			 * don't have to do it here.
 			 */
-			ret = split_symref_update(refs, update,
+			ret = split_symref_update(update,
 						  referent.buf, transaction,
 						  affected_refnames, err);
 			if (ret)