[IPV6]: remove duplicate call to proc_net_remove

The file /proc/net/if_inet6 is removed twice.
First time in:
        inet6_exit
             ->addrconf_cleanup
And followed a few lines after by:
        inet6_exit
             -> if6_proc_exit

Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 348bd8d..1bd8d81 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -4288,8 +4288,4 @@
 	del_timer(&addr_chk_timer);
 
 	rtnl_unlock();
-
-#ifdef CONFIG_PROC_FS
-	proc_net_remove(&init_net, "if_inet6");
-#endif
 }