sched/fair: Remove unused 'next_buddy_marked' local variable in check_preempt_wakeup_fair()

This variable became unused in:

    5e963f2b ("sched/fair: Commit to EEVDF")

Signed-off-by: Wang Jinchao <wangjinchao@xfusion.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/202312141319+0800-wangjinchao@xfusion.com