tipc: Eliminate timestamp from link protocol messages

Removes support for the timestamp field of TIPC's link protocol messages.

This field was previously used to hold an OS-dependent timestamp value
that was used to assist in debugging early versions of TIPC. The field
has now been deemed unnecessary and has been removed from the latest TIPC
specification. This change has no impact on the operation of TIPC since
the field was set by TIPC, but never referenced.

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