The ->preemptible field in rcu_data is only initialized in the function
rcu_init_percpu_data(), and never used.  This commit therefore removes
this field.
Signed-off-by: NIulia Manda <iulia.manda21@gmail.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>