x86, 386 removal: Remove CONFIG_X86_POPAD_OK

The check_popad() routine tested for a 386-specific bug, and never
actually did anything useful with it anyway other than print a
message.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1354132230-21854-8-git-send-email-hpa@linux.intel.com