Remove incorrect HINT for use of ALTER FOREIGN TABLE on the wrong relkind.

Per discussion, removing the hint seems better than correcting it because
the adjacent analogous cases in RenameRelation don't have any hints, and
nobody seems to have missed 'em.

Shigeru Hanada

src/backend/commands/tablecmds.c

@@ -2247,8 +2247,7 @@ RenameRelation(Oid myrelid, const char *newrelname, ObjectType reltype)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("\"%s\" is not a foreign table",
-						RelationGetRelationName(targetrelation)),
-				 errhint("Use ALTER FOREIGN TABLE instead.")));
+						RelationGetRelationName(targetrelation))));
 
 	/*
 	 * Don't allow ALTER TABLE on composite types. We want people to use ALTER