Revert "System adapted to new workqueue 3.7"

This reverts commit 5fcb4cecfa5900c8d5aa99c0e1f9573ce885ffd0.
Revert "workqueue: gut system_nrt[_freezable]_wq()"

This reverts commit 8d2eb54fe6a1712af738e7f1e8d9b1d4fbf4cc89.