sched: remove temporary demand fixups in fixup_busy_time()

On older kernel versions p->on_rq was a binary value that did not
allow distinguishing between enqueued and migrating tasks. As a result
fixup_busy_time would have to do temporary load adjustments to ensure
that update_history does not do incorrect demand adjustments for
migrating tasks. Since p->on_rq can now be used make a distinction
between migrating and enqueued tasks, there is no need to do these
temporary load calculations. Instead make sure update_history() only
does load adjustments on enqueued tasks.

Change-Id: I1f800ac61a045a66ab44b9219516c39aa08db087
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>