The destroy callback in wlr_touch_impl has been removed. The function
`wlr_touch_finish` has been introduced to clean up the resources owned by a
wlr_touch.
`wlr_input_device_destroy` no longer destroys the wlr_touch, attempting to
destroy a wlr_touch will result in a no-op.
The field `name` has been added to the wlr_touch_impl to be able to identify
a given wlr_touch device.