MINOR: sched: do not punish self-waking tasklets anymore

MINOR: sched: do not punish self-waking tasklets anymore

Nowadays due to yield etc, it's counter-productive to permanently
punish self-waking tasklets, let's abandon this principle as it prevent
finer task priority handling.

We continue to check for the TASK_SELF_WAKING flag to place a task
into TL_BULK in case some code wants to make use of it in the future
(similarly to TASK_HEAVY), but no code sets it anymore. It could
possible make sense in the future to replace this flag with a one-shot
variant requesting low-priority.