This one is an interesting case. It was easier to simply switch
to AdwPreferencesPage than actually port all the GtkFrames in
there.
In addition to that, the mouse test page now uses a GtkPicture
instead of a GtkImage, and the GtkDrawingArea API changes are
reflected in the code.
It seems like (at least some versions of) gdk don't set
GDK_SOURCE_TOUCHPAD on synaptics devices. In this case though, we
don't need the additional check. Just knowing if there's any device
being driven by this X driver is enough.
https://bugzilla.gnome.org/show_bug.cgi?id=784266
Since we don't support the synaptics driver anymore we shouldn't show
the touchpad section in that case. In addition, emit a warning so that
this system mis-configuration is easier to diagnose.
https://bugzilla.gnome.org/show_bug.cgi?id=764257
