tipc: remove obsolete flush of stale reassembly buffer

Each link instance has a periodic job checking if there is a stale
ongoing message reassembly associated to the link. If no new
fragment has been received during the last 4*[link_tolerance] period,
it is assumed the missing fragment will never arrive. As a consequence,
the reassembly buffer is discarded, and a gap in the message sequence
occurs.

This assumption is wrong. After we abandoned our ambition to develop
packet routing for multi-cluster networks, only single-hop packet
transfer remains as an option. For those, all packets are guaranteed
to be delivered in sequence to the defragmentation layer. Any failure
to achieve sequenced delivery will eventually lead to link reset, and
the reassembly buffer will be flushed anyway.

So we just remove this periodic check, which is now obsolete.

Signed-off-by: Erik Hugne <erik.hugne@ericsson.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
[PG: also delete get/inc_timer count, since they are now unused]
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>