rcu: Remove redundant "if" condition from rcu_gp_is_expedited()

Because rcu_expedited_nesting is initialized to 1 and not decremented
until just before init is spawned, rcu_expedited_nesting is guaranteed
to be non-zero whenever rcu_scheduler_active == RCU_SCHEDULER_INIT.
This commit therefore removes this redundant "if" equality test.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>