Revert "Move packet-kerberos.c to the dirty dissectors because it generates warnings (at least on NetBSD), presumably due to our use of -Wc++-compat:"

This reverts commit d4ff430b4dc5cf0e3efaabd2ef53778070def558.

Change-Id: Icb0907e649555237b4a86f9f651ec4df8d79d99b
Reviewed-on: https://code.wireshark.org/review/5975
Reviewed-by: Stephen Fisher <sfisher@sdf.org>