tipc: Eliminate obsolete routine for handling routed messages

Eliminates a routine that is used in handling messages arriving from
another cluster or zone. Such messages can no longer be received by TIPC
now that multi-cluster and multi-zone network support has been eliminated.

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>