sched/fair: Fix stale comments referring to removed CFS concepts

A few comments still describe the pre-EEVDF CFS world:

 - sysctl_sched_base_slice is documented as "Minimal preemption
   granularity for CPU-bound tasks".  That was the wording of the old
   sysctl_sched_min_granularity, renamed in commit e4ec3318a1
   ("sched/debug: Rename sysctl_sched_min_granularity to
   sysctl_sched_base_slice").  Under EEVDF it is the default base time
   slice / request size (r_i) used to compute the virtual deadline, as
   documented in update_deadline().

 - Two comments still mention sched_slice(), which was removed when the
   fair class committed to EEVDF in commit 5e963f2bd4 ("sched/fair:
   Commit to EEVDF").  The dequeue-path comment should simply refer to
   the task's slice (se->slice); the forced-idle comment describes the
   slice accounting now performed by __entity_slice_used(), which is the
   function actually used right below it.

No functional changes.

[ mingo: Ported to a more recent scheduler base ]

Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260629030200.3165589-1-zhanxusheng@xiaomi.com

kernel/sched/fair.c

@@ -73,7 +73,10 @@
 unsigned int sysctl_sched_tunable_scaling = SCHED_TUNABLESCALING_LOG;
 
 /*
- * Minimal preemption granularity for CPU-bound tasks:
+ * Default base time slice (request size r_i) for SCHED_NORMAL/SCHED_BATCH:
+ *
+ * Under EEVDF this is the request size used to compute the virtual
+ * deadline; see update_deadline().
  *
  * (default: 0.70 msec * (1 + ilog(ncpus)), units: nanoseconds)
  */
@@ -14676,7 +14679,7 @@ static inline void task_tick_core(struct rq *rq, struct task_struct *curr)
 	 * if the sibling is forced idle, then trigger schedule to
 	 * give forced idle task a chance.
 	 *
-	 * sched_slice() considers only this active rq and it gets the
+	 * __entity_slice_used() considers only this active rq and it gets the
 	 * whole slice. But during force idle, we have siblings acting
 	 * like a single runqueue and hence we need to consider runnable
 	 * tasks on this CPU and the forced idle CPU. Ideally, we should