rcu/nocb: Fix segcblist state machine stale comments about timers

The (de-)offloading process used to take care about the NOCB timer when
it depended on the per-rdp NOCB locking. However this isn't the case
anymore for a long while. It can now safely be armed and run during the
(de-)offloading process, which doesn't care about it anymore.

Update the comments accordingly.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>