ws: Fix invalid check for HTTP upgrade

Leave these checks to the WebSocket code. The code here was
invalid anyway, and checked whether both headers were missing.

Closes #534
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
ws: Don't use g_warning for WebSocket connection errors

g_warning() should be for local problems. g_message() is more
appropriate for warning about bad callers.

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>