netlink: Remove smp_read_barrier_depends() from comment

Now that smp_read_barrier_depends() has been de-emphasized, the less
said about it, the better.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Cc: Florian Westphal <fw@strlen.de>
Cc: <netfilter-devel@vger.kernel.org>
Cc: <coreteam@netfilter.org>

include/linux/netfilter/nfnetlink.h

@@ -67,8 +67,7 @@ static inline bool lockdep_nfnl_is_held(__u8 subsys_id)
  * @ss: The nfnetlink subsystem ID
  *
  * Return the value of the specified RCU-protected pointer, but omit
- * both the smp_read_barrier_depends() and the READ_ONCE(), because
- * caller holds the NFNL subsystem mutex.
+ * the READ_ONCE(), because caller holds the NFNL subsystem mutex.
  */
 #define nfnl_dereference(p, ss)					\
 	rcu_dereference_protected(p, lockdep_nfnl_is_held(ss))