net/dsa/tag_8021q.c: remove superfluous headers

tag_8021q.c hasn't use any macro or function declared in linux/if_bridge.h.
Thus, these files can be removed from tag_8021q.c safely without
affecting the compilation of the ./net/dsa module
Signed-off-by: Mianhan Liu <liumh1@shanghaitech.edu.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/tag_8021q.c

@@ -6,7 +6,6 @@
  * dsa_8021q_netdev_ops is registered for API compliance and not used
  * directly by callers.
  */
-#include <linux/if_bridge.h>
 #include <linux/if_vlan.h>
 #include <linux/dsa/8021q.h>