Eliminate proto_tree_add_text from some of the dissectors.

Other minor cleanups while in the area.

Change-Id: I99096ade9c69a4c148962d45bb6b0bd775040ba1
Reviewed-on: https://code.wireshark.org/review/4020
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>