Remove some proto_item_append_string

Remove some proto_item_append_string

These calls to proto_item_append_string were not taking into account all
of the special treatment needed to use it, so proto_item_append_text
(or similar) was probably intended.

Change-Id: I5d1f092f8162a87d30fc8dc694f6124dc81372b5
Reviewed-on: https://code.wireshark.org/review/15575
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Jeff Morriss <jeff.morriss.ws@gmail.com>
Reviewed-by: Michael Mann <mmann78@netscape.net>