sched/walt: Remove fixup_walt_sched_stats sched_class method

fixup_walt_sched_stats method in sched_class was required because
fair class need to handle it differently when CFS_BANDWIDTH feature
is enabled. Since that is gone, we can remove this method and reduce
WALT footprint in other files.

Change-Id: Ia20c4accf9beb9f79554636c8faced3d31358622
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
[clingutla@codeaurora.org: Resolved trivial merge conflicts]
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
Signed-off-by: Shaleen Agrawal <shalagra@codeaurora.org>