sched/headers: Remove comment referring to rq::cpu_load, since this has been removed

There is a comment that refers to cpu_load, however, this cpu_load was
removed with:

  55627e3c ("sched/core: Remove rq->cpu_load[]")

... back in 2019. The comment does not make sense with respect to this
removed array, so remove the comment.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231010155744.1381065-1-colin.i.king@gmail.com