x86: remove page_fault_trace

Old debugging code that is not really needed anymore. If someone
wants it it would be better replaced with a systemtap script or
kprobe.

This avoids a potential cache miss during page fault processing.

[ mingo: arch/x86 adaptation ]

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>