Removes the id->row mapping. It was broken as the indices weren't updated
when a row was added or removed.
Stop exposing Device::id through dbus, just store it in the interface
class.
* It's redundant as it's part of the interface definition
* If we keep it it will save us quite some dbus round-trips
* It will be reliable, as nowadays id() sometimes QString() if the dbus
connection is invalid.
REVIEW: 124158
43451d6ae1