base_ref_store_init(): remove submodule argument

This is another step towards weakening the 1:1 relationship between
ref_stores and submodules.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/refs.c b/refs.c
index 07959ff..05af56b 100644
--- a/refs.c
+++ b/refs.c
@@ -1477,8 +1477,7 @@ struct ref_store *get_ref_store(const char *submodule)
 }
 
 void base_ref_store_init(struct ref_store *refs,
-			 const struct ref_storage_be *be,
-			 const char *submodule)
+			 const struct ref_storage_be *be)
 {
 	refs->be = be;
 }