Remove get_attidentity()

All existing uses can get this information more easily from the
relation descriptor, so the detour through the syscache is not
necessary.

Reviewed-by: Michael Paquier <michael@paquier.xyz>

src/backend/utils/cache/lsyscache.c

@@ -821,38 +821,6 @@ get_attnum(Oid relid, const char *attname)
 		return InvalidAttrNumber;
 }
 
-/*
- * get_attidentity
- *
- *		Given the relation id and the attribute name,
- *		return the "attidentity" field from the attribute relation.
- *
- *		Returns '\0' if not found.
- *
- *		Since no identity is represented by '\0', this can also be used as a
- *		Boolean test.
- */
-char
-get_attidentity(Oid relid, AttrNumber attnum)
-{
-	HeapTuple	tp;
-
-	tp = SearchSysCache2(ATTNUM,
-						 ObjectIdGetDatum(relid),
-						 Int16GetDatum(attnum));
-	if (HeapTupleIsValid(tp))
-	{
-		Form_pg_attribute att_tup = (Form_pg_attribute) GETSTRUCT(tp);
-		char		result;
-
-		result = att_tup->attidentity;
-		ReleaseSysCache(tp);
-		return result;
-	}
-	else
-		return '\0';
-}
-
 /*
  * get_atttype
  *