KVM: Remove memory alias support

As advertised in feature-removal-schedule.txt.  Equivalent support is provided
by overlapping memory regions.

Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 863920f..a21a86e 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -576,7 +576,6 @@
  * Using the cached information from sp->gfns is safe because:
  * - The spte has a reference to the struct page, so the pfn for a given gfn
  *   can't change unless all sptes pointing to it are nuked first.
- * - Alias changes zap the entire shadow cache.
  */
 static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
 			    bool clear_unsync)
@@ -611,7 +610,7 @@
 			return -EINVAL;
 
 		gfn = gpte_to_gfn(gpte);
-		if (unalias_gfn(vcpu->kvm, gfn) != sp->gfns[i] ||
+		if (gfn != sp->gfns[i] ||
 		      !is_present_gpte(gpte) || !(gpte & PT_ACCESSED_MASK)) {
 			u64 nonpresent;