Revert "kernel/sched: Modify initial boot task idle setup"

This reverts commit 3569ad59 which is
commit cff9b233

 upstream.

Joel writes:
	Let us drop this patch because it caused new tasks-RCU warnings (both
	normal and rude tasks RCU) in my stable test rig. We are discussing
	the "right fix" and at that time a backport can be done.

Reported-by: Joel Fernandes <joel@joelfernandes.org>
Link: https://lore.kernel.org/r/CAEXW_YT6bH70M1TF2TttB-_kP=RUv_1nsy_sHYi6_0oCrX3mVQ@mail.gmail.com
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>