sched: Remove set_need_resched()

The last user is gone now, so we can safely remove this function.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <bitbucket@online.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>