Because RCU-tasks exists only in PREEMPT kernels and because RCU-sched
no longer exists in PREEMPT kernels, it is no longer necessary for the
rcu_note_voluntary_context_switch() macro to do anything for !PREEMPT
kernels.  This commit therefore removes !PREEMPT-related code from
this macro, namely, the rcu_all_qs().
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>