Eliminate proto_tree_add_text from some dissectors.

Other minor cleanup while in the area.

Change-Id: Id8d957d3d68a2e3dd5089f490bd59d773e1be967
Reviewed-on: https://code.wireshark.org/review/3427
Reviewed-by: Michael Mann <mmann78@netscape.net>
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>