Revert "rtnetlink: add guard for RTNL"

This reverts commit 464eb03.

Once we have a per-netns RTNL, we won't use guard(rtnl).

Also, there's no users for now.

  $ grep -rnI "guard(rtnl" || true
  $

Suggested-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/netdev/CANn89i+KoYzUH+VPLdGmLABYf5y4TW0hrM4UAeQQJ9AREty0iw@mail.gmail.com/
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

include/linux/rtnetlink.h

@@ -7,7 +7,6 @@
 #include <linux/netdevice.h>
 #include <linux/wait.h>
 #include <linux/refcount.h>
-#include <linux/cleanup.h>
 #include <uapi/linux/rtnetlink.h>
 
 extern int rtnetlink_send(struct sk_buff *skb, struct net *net, u32 pid, u32 group, int echo);
@@ -47,8 +46,6 @@ extern int rtnl_is_locked(void);
 extern int rtnl_lock_killable(void);
 extern bool refcount_dec_and_rtnl_lock(refcount_t *r);
 
-DEFINE_LOCK_GUARD_0(rtnl, rtnl_lock(), rtnl_unlock())
-
 extern wait_queue_head_t netdev_unregistering_wq;
 extern atomic_t dev_unreg_count;
 extern struct rw_semaphore pernet_ops_rwsem;