Protocol : Added destructor to wl_data_device interface

[Pekka Paalanen: removed trailing whitespace, adjust bz link.]

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=81745


Signed-off-by: kabeer khan <kabeer.khan@samsung.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>