Revert "sched,fair: Alternative sched_slice()"

This reverts commit ae7fe479 which
showed up in 5.10.36 and broke the abi.  It should not be needed in
Android systems at this time so it is safe to revert.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I69f1885bb0d25ebbaa52422d6c238f13fbe0a0f3