Don't try and run checkAPIs.pl on deleted files

It fails, for obvious reasons, and makes it impossible to commit the removal of
c/h files.

Change-Id: Ifcd067f8959684e2e0191983fd60fb94ae86bca3
Reviewed-on: https://code.wireshark.org/review/3401
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Evan Huus <eapache@gmail.com>