packet-PROTOABBREV.c: Update re #includeusage

- packet.h should be first Wireshark #include
  after config.h and "system" includes.
- '#include <glib.h>' not needed.

Change-Id: Ibec076818f3f509aabb4d240e939ef719f3798d6
Reviewed-on: https://code.wireshark.org/review/5939
Reviewed-by: Bill Meier <wmeier@newsguy.com>