sched/fair: Cleanup pick_task_fair()'s curr

With 4c456c9a ("sched/fair: Remove unused 'curr' argument from
pick_next_entity()") curr is no longer being used, so no point in
clearing it.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Tested-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lkml.kernel.org/r/20240727105028.614707623@infradead.org