time: Add xtime, wall_to_monotonic to feature-removal-schedule

They aren't really features, but fair warning to out of tree
driver folks who might be accessing these variables.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
CC: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <1268434560-2677-1-git-send-email-johnstul@us.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>