Do not wait for sleeping in init_threads()

We can't do it with full guarantee anyway because
there is always a possible race between the setting of
state to THREAD_SLEEPING and actual sleeping.

So just remove the not perfect code to avoid misunderstandings.
This reflects what we have done in wake_sleeping_threads() in
the previous patch.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>