rcu-tasks: Remove grace-period fast-path rcu-tasks helper

Now that the grace-period fast path can only happen during the
pre-scheduler portion of early boot, this fast path can no longer block
run-time RCU Tasks and RCU Tasks Trace grace periods.  This commit
therefore removes the conditional cond_resched_tasks_rcu_qs() invocation.

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