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

../../asn1/kerberos/packet-kerberos-template.c: In function
'read_keytab_file':
../../asn1/kerberos/packet-kerberos-template.c:497:10: warning: request
for implicit conversion from 'gpointer' to 'struct enc_key_t *' not
permitted in C++
../../asn1/kerberos/packet-kerberos-template.c:518:21: warning: request
for implicit conversion from 'gpointer' to 'char *' not permitted in C++
../../asn1/kerberos/packet-kerberos-template.c: In function
'decrypt_krb5_data':
../../asn1/kerberos/packet-kerberos-template.c:570:3: warning: enum
conversion when passing argument 3 of 'krb5_crypto_init' is invalid in
C++/usr/include/krb5/krb5-protos.h:1208:1: note: expected 'krb5_enctype'
but argument is of type 'int'
../../asn1/kerberos/packet-kerberos-template.c:581:13: warning: request
for implicit conversion from 'gpointer' to 'guint8 *' not permitted in
C++
../../asn1/kerberos/packet-kerberos-template.c:596:13: warning: request
for implicit conversion from 'gpointer' to 'char *' not permitted in C++

Change-Id: I17c10fc1df2685ec2e2c1b00cd3b81f62e09c829
Reviewed-on: https://code.wireshark.org/review/5886
Reviewed-by: Stephen Fisher <sfisher@sdf.org>