RDS: don't pretend to use cpu notifiers

It looks like an attempt to use CPU notifier here which was never
completed. Nobody tried to wire it up completely since 2k9. So I unwind
this code and get rid of everything not required. Oh look! 19 lines were
removed while code still does the same thing.

Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Tested-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>