Remove private mutators for context enctypes

Remove private mutators for context enctypes

krb5_set_default_in_tkt_ktypes() and krb5_set_default_tgs_ktypes() are
not part of the API and are only used in test programs, so remove
them.  Also remove the now-unused in_tkt_etypes field from
krb5_context.  Update test suite consumers.

Fix a minor bug wherein the etinfo executable would not correctly
print its usage text.

[ghudson@mit.edu: adapted some tests rather than remove them]