kerberos: drop weird, superfluous assignment in query function

goa_kerberos_identity_inquiry_answer_query has this strange code:

g_return_if_fail (inquiry == kerberos_query->inquiry);
...
inquiry = kerberos_query->inquiry;

It's completely redundant and makes no sense so drop it.

https://bugzilla.gnome.org/show_bug.cgi?id=739593