sched/fair: Cleanup pick_task_fair() vs throttle

Per 54d27365 ("sched/fair: Prevent throttling in early
pick_next_task_fair()") the reason check_cfs_rq_runtime() is under the
'if (curr)' check is to ensure the (downward) traversal does not
result in an empty cfs_rq.

But then the pick_task_fair() 'copy' of all this made it restart the
traversal anyway, so that seems to solve the issue too.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Tested-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lkml.kernel.org/r/20240727105028.501679876@infradead.org