Add a 'Removed' DeviceType
The X.org server sends HierarchyChanged events with device type set to zero for devices that were removed. Since "DeviceType" is used in an enum, this means that only values of that enum can appear. This is not allowed by the spec, but it is what happens in reality. Thus, this commit changes xinput.xml to describe reality by adding "Removed" as a new "DeviceType".