Revert "sched: fix single cpu running issue"

Previously, walt sched clusters prepared with empty cpumask for
single core bootup, which causes panic. Now sched clusters preparation
avoids empty cpu mask, so the commit 'c94eae6f("sched: fix single
cpu running issue")' becomes stale now, and it is adding extra
overhead in scheduler hotpaths, so remove it.

Change-Id: Ie6167e7c148d35b94fb8101caea16282d6d133fc
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>