tipc: remove redundant call to tipc_node_remove_conn

tipc_node_remove_conn may be called twice if shutdown() is
called on a socket that have messages in the receive queue.
Calling this function twice does no harm, but is unnecessary
and we remove the redundant call.

Signed-off-by: Erik Hugne <erik.hugne@ericsson.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Acked-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>