I noticed this while making investigations into the tbench
regressions.  Please apply.

sched: Remove hrtick_resched() extern decl.

This function was removed by 31656519
("sched, x86: clean up hrtick implementation").
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>