Revert "kthread_work: wake up worker only when the worker is idle"

This reverts commit 3023a270a6b515e3ab5144d4bfd7a59479bc16fa.
Revert "softirq: Use hotplug thread infrastructure"

This reverts commit 4e5c67929334eb788b76537331b95e6b6c72bf1e.
Revert "Hotplug thread infrastructure"

This reverts commit 6a25ce64d8a277d0abb2ded513d542422ad882bd.