tipc: remove protocol message queue

TIPC protocol message queue is intended to save one protocol message
when bearer is congested so that the message stored in the queue can
be immediately transmitted when bearer congestion is released. However,
as now the protocol queue has no mission any more with the removal of
bearer congestion mechanism, it should be removed.

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