The Refresh D-Bus method could be used by clients to force re-reading
the state of batteries in the upower backends. This is not needed as
all the backends should be sending events when their states changes,
removing the need for an explicit refresh.

This is also a potential security problem if applications keep on
refreshing their data.

We now only allow access to the Refresh() method if the daemon was
started in debugging mode. This should make it clearer that it is a
debug tool.

Also remove a mention of the never implemented refresh-power-source
polkit authorisation.