x86: remove unused macro

Mr. Grep says warn_if_not_ulong() is not used anymore anywhere
in the code. So, we remove it.

Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>