Revert "kernel/cpu.c: Add comment for priority in cpu_hotplug_pm_callback"

This reverts commit fdb96c1c75b17468f272b7b8482e6c57488764d6.
Revert "mm/hotplug: correctly setup fallback zonelists when creating new pgdat"

This reverts commit 76479da8dab806d18bc0319a5758787bfb0c7520.
Revert "kernel/cpu.c: document clear_tasks_mm_cpumask()"

This reverts commit 7e90b08c9b579d6ca8fa123c0952acb0ee4c7a2a.
Revert "cpu: introduce clear_tasks_mm_cpumask() helper"

This reverts commit dd1c09155f65f408bc3003a8be13514d8c018c6c.