sched: Remove some dummy functions

No one will call those functions if CONFIG_SCHED_DEBUG=n.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/5135A748.3050206@huawei.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>