audiod: Get rid of the audiod task.

It's simpler to start/stop the decoders from status_pre_select()
because this is the point where we get the recent status info from
para_server.

In particular, this allows to kill the min_delay crap in
the audiod_pre_select() which now gets called from
status_pre_select(). Rename it to start_stop_decoders() as
this is what that function does.