packet-PROTOABBREV.c: various minor changes:

- Specify that proto_register...() and proto_reg_handoff...() prototypes are required;
- Indicate that certain #includes should be used only as needed;
- Don't use CamelCase (or CAPS) in variable names;
- Do some reformatting of certain lines;
- Futz hf[] array entry so checkAPIs and checkhf tests don't fail.

Change-Id: Ie03846f4bebd2a9bece464c85cc3c2ef46dd4fe5
Reviewed-on: https://code.wireshark.org/review/3724
Reviewed-by: Bill Meier <wmeier@newsguy.com>
Reviewed-by: Evan Huus <eapache@gmail.com>