sched/fair: Remove unused parameter idle of _nohz_idle_balance()

After commit 7a82e5f5 ("sched/fair: Merge for each idle cpu loop of ILB"),
_nohz_idle_balance()'s 'idle' parameter is not used anymore, so we can remove it.

Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20220803130223.70419-1-jiahao.os@bytedance.com