Avoid using internal APIs in sim_client

Avoid using internal APIs in sim_client

In sim_client.c, remove the calls to krb5_gen_portaddr() and
krb5_gen_replay_name() as they don't do anything after commit
dcb853ac32779b173f39e19c0f24b0087de85771.  Remove them, and include
krb5.h plus appropriate system headers rather than k5-int.h.

Also use a subkey when negotiating the auth context.  Kerberos
application protocols should generally use subkeys to prevent
cross-connection replay attacks.