backend/wayland: fix undefined reference to wlr_wl_input_device_get_seat
Amend b7e9ad79 to remove wlr_wl_input_device_get_seat definition.
Closes: #3611 (closed)
Amend b7e9ad79 to remove wlr_wl_input_device_get_seat definition.
Closes: #3611 (closed)