revert(3p/git): Revert merge of git upstream at v2.26.2

This causes cgit to serve error pages, which is undesirable.

This reverts commit 5229c9b232, reversing
changes made to f2b211131f.

third_party/git/replace-object.h

@@ -24,17 +24,12 @@ const struct object_id *do_lookup_replace_object(struct repository *r,
  * name (replaced recursively, if necessary).  The return value is
  * either sha1 or a pointer to a permanently-allocated value.  When
  * object replacement is suppressed, always return sha1.
- *
- * Note: some thread debuggers might point a data race on the
- * replace_map_initialized reading in this function. However, we know there's no
- * problem in the value being updated by one thread right after another one read
- * it here (and it should be written to only once, anyway).
  */
 static inline const struct object_id *lookup_replace_object(struct repository *r,
 							    const struct object_id *oid)
 {
 	if (!read_replace_refs ||
-	    (r->objects->replace_map_initialized &&
+	    (r->objects->replace_map &&
 	     r->objects->replace_map->map.tablesize == 0))
 		return oid;
 	return do_lookup_replace_object(r, oid);