Drop KIO::AccessManager
This is a QNetworkAccessManager subclass that uses KIO workers to implement network access.
It provides some integration with various connection settings and a cookie jar.
However it is barely used any more and the provided integration settings aren't useful for applications typically.
Furthermore going forward we want to implement kio_http based on QNetworkAccessManager, meaning a QNetworkAccessManager based on kio_http wouldn't make much sense any more