Revert "mutex: dynamically disable mutex spinning at high load"

This reverts commit 58012c586dbf59e69bd1c056f6660a7cd307b33c.
Revert "mutex: restrict mutex spinning to only one task per mutex"

This reverts commit 5275c1c77731f5e284172bd530437bb9893a1560.
Revert "mutex: Make more scalable by doing less atomic operations"

This reverts commit a6d727f50225c9dd818a7ba6664876cc4b71cb8f.
Revert "sched: don't call task_group() many times in set_task_rq()"

This reverts commit a6f08d20ec2728b54bce73cb33d419a1a5e427f5.