wrong hint message for ALTER FOREIGN TABLE

I noticed that ALTER FOREIGN TABLE RENAME TO emits a wrong hint message 
if the object was not a foreign table.  ISTM that the hint message is 
not necessary there. Attached patch removes the hint message.

Steps to reproduce the situation:

postgres=# CREATE FOREIGN TABLE foo () SERVER file_server;
postgres=# ALTER FOREIGN TABLE foo RENAME TO bar;
ERROR:  "foo" is not a foreign table
HINT:  Use ALTER FOREIGN TABLE instead.

Regards,
-- 
Shigeru Hanada