At some point we crossed the streams... In a short timespan we had
1f00aba92c32 merged, pushing WacomDevice to a common parent object,
and dcaa45fc0c199 implementing device grouping for X11.
The latter did not rely on the former, and just happened to
merge/compile without issues, but would promptly trigger a crash
whenever the API would be used.
Drop all traces of the WacomDevice internal to MetaInputDeviceX11.
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1183