wl-input: Remove the wl_touch code

Clayland doesn't currently use any touch support. If we want to add it
back later then it will be easier to copy in code from the lastest
Weston rather than using the old libwayland-server code.
Incorporate the cwl_* structs into the corresponding Clayland* struct

Instead of having a separate struct for the code borrowed from
libwayland server the data from them is now directly incorporated in
the corresponding Clayland* struct. This includes adding a
ClaylandPointer struct and a ClaylandDataSource struct.