Revert "KVM: x86: apply guest MTRR virtualization on host reserved pages"

This reverts commit fd717f11.
It was reported to cause Machine Check Exceptions (bug 104091).

Reported-by:  <harn-solo@gmx.de>
Cc: stable@vger.kernel.org # 4.2+
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>