sched/nohz: Update idle load-balancing (ILB) comments

 - Fix incorrect/misleading comments,

 - clarify some others,

 - fix typos & grammar,

 - and use more consistent style throughout.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Link: https://lore.kernel.org/r/20231006102518.2452758-2-mingo@kernel.org