tipc: Prune unused data structures from configuration service

Eliminate some unused data structures in the TIPC
configuration service that relate to the handling of link
subscriptions, which were not supported when TIPC 1.5 was
introduced.  If and when support for link subscriptions is
offered in TIPC, these elements may need to be re-introduced.

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>