tshark: endpoints statistics are not supported for now, do not list them in -z

Move statistics registration to "GUI" callback registration

Change-Id: Id27c049dc8f91d311e9231342ae40749ca0ff5fc
Reviewed-on: https://code.wireshark.org/review/6151
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>
Petri-Dish: Pascal Quantin <pascal.quantin@gmail.com>
Reviewed-by: Michael Mann <mmann78@netscape.net>