packet-git.c says it was copied from packet-pop, but that doesn't mean
packet-git is for "RFC 1939" (POP3), so remove that comment.

Change-Id: Ia78ea18beb1a13ab0ad1ad5a87f7b5a887fad918
Reviewed-on: https://code.wireshark.org/review/6041
Reviewed-by: Stephen Fisher <sfisher@sdf.org>