sched: Rollback upstream backport

 * There are some stability issues under certain loads with this
   patchset. Rollback until we can revisit.

Revert "[backport] sched_rt: Upstream fixes"

This reverts commit 3aef4fdd36c3db6f5df88629ab0a9d6c42bae26c.

Revert "[backport] sched: Misc upstream scheduler improvements"

This reverts commit fa16d20f1c90bb0d7955b194d450891de680494e.

Revert "[backport]: sched: Load-based CPU boosting"

This reverts commit 54d5731ffe5a109691de3f61eeda14bd42942325.

Revert "sched: Remove get_online_cpus() usage"

This reverts commit 86b047357013e1d5c5547fd6d466dd75b90afc81.

Change-Id: I8bb638023a95df7ae7a44b06017c0190985e3f22