raw_object_store: drop extra pointer to replace_map

We store the replacement data in an oidmap, which is itself a pointer in
the raw_object_store struct. But there's no need for an extra pointer
indirection here. It is always allocated and initialized along with the
containing struct, and we never check it for NULL-ness.

Let's embed the map directly in the struct, which is simpler and avoids
extra pointer chasing.

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

replace-object.h

@@ -47,7 +47,7 @@ static inline const struct object_id *lookup_replace_object(struct repository *r
 {
 	if (!replace_refs_enabled(r) ||
 	    (r->objects->replace_map_initialized &&
-	     oidmap_get_size(r->objects->replace_map) == 0))
+	     oidmap_get_size(&r->objects->replace_map) == 0))
 		return oid;
 	return do_lookup_replace_object(r, oid);
 }