Remove unused macro

Use was removed in 6d46f4783efe457f74816a75173eb23ed8930020 but
definition was forgotten.

src/backend/access/hash/hashpage.c

@@ -48,16 +48,6 @@ static void _hash_splitbucket(Relation rel, Buffer metabuf,
 static void log_split_page(Relation rel, Buffer buf);
 
 
-/*
- * We use high-concurrency locking on hash indexes (see README for an overview
- * of the locking rules).  However, we can skip taking lmgr locks when the
- * index is local to the current backend (ie, either temp or new in the
- * current transaction).  No one else can see it, so there's no reason to
- * take locks.  We still take buffer-level locks, but not lmgr locks.
- */
-#define USELOCKING(rel)		(!RELATION_IS_LOCAL(rel))
-
-
 /*
  *	_hash_getbuf() -- Get a buffer by block number for read or write.
  *