rcu: Remove obsolete ->dynticks_fqs and ->cond_resched_completed

The rcu_data structure's ->dynticks_fqs is incremented but never
accesses.  Its ->cond_resched_completed field isn't used at all.
This commit therefore removes both fields.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>