Now that the return type of rcu_batches_completed() and friends matches
that of the rcu_torture_ops structure's ->completed field, the wrapper
functions can be deleted.  This commit carries out that deletion, while
also wiring "sched"'s ->completed field to rcu_batches_completed_sched().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>