Remove useless x86 options that were always hardcoded on.

ARCH_X86_HAVE_MMX, ARCH_X86_HAVE_SSE, ARCH_X86_HAVE_SSE2,
and ARCH_X86_HAVE_SSE3 were all always on. There are no longer any makefiles
or code that are conditional on any of these, so let's just remove them
rather than encourage anyone to mess with knobs that don't work.

Change-Id: I5ee095e8041eecff4554ad4801894fbfca69093f