revert:

| commit 47001d60
| Author: Thomas Gleixner <tglx@linutronix.de>
| Date:   Tue Apr 1 19:45:18 2008 +0200
|
|     x86: tsc prevent time going backwards

it has been identified to cause suspend regression - and the
commit fixes a longstanding bug that existed before 2.6.25 was
opened - so it can wait some more until the effects are better
understood.
Signed-off-by: Ingo Molnar <mingo@elte.hu>