Eliminate proto_tree_add_text from packet-fcels.c

Change-Id: Iac322d7c7d66d90994bce377dd8c7e39a36466cf
Reviewed-on: https://code.wireshark.org/review/5003
Petri-Dish: Michael Mann <mmann78@netscape.net>
Reviewed-by: Michael Mann <mmann78@netscape.net>