Revert "[PATCH] x86-64: Fix up handling of non canonical user RIPs"

This reverts commit c33d4568

.

Andrew Clayton and Hugh Dickins report that it's broken for them and
causes strange page table and slab corruption, and spontaneous reboots.

Let's get it right next time.

Cc: Andrew Clayton <andrew@rootshell.co.uk>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>