Revert "ANDROID: sched/walt: Fix compilation issue for x86_64"

This reverts commit a56900fa.

The compilation issue mentioned in commit 'a56900fa ("ANDROID:
sched/walt: Fix compilation issue for x86_64")' is not needed, as
cumulative_runnable_avg is tracked seperately in walt_sched_stats
structure. And the cumulative_runnable_avg value is updated in
walt_sched_stats tracking functions itself, so reverting the above
commit.

Change-Id: I3003c93d64a95606310af400f210d8633c1012d2
Signed-off-by: Blagovest Kolenichev <bkolenichev@codeaurora.org>