Clean up enabling/disabling NTLM and Basic auth types

The use-ntlm property has been deprecated for ages. Use
soup_session_add_feature_by_type() to enable NTLM instead. And use
soup_session_disable_feature_by_type() to *disable* Basic auth, if we're
not supposed to be using it. Otherwise, it gets in the way of our GSSAPI
hacks.