Revert "arm64/arm: xen: enlighten: Fix KPTI checks"

This reverts commit a00a293d which is
commit 20f3b8ea upstream.

It breaks the Android ABI and we do not care about Xen on Android, so it
is safe to revert.

Bug: 161946584
Change-Id: I4bf8a87650256a5f4b2faee626557604631ee286
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>