yadif: remove plugin, there's now deinterlace method=yadif
Plugin code was still the GPL version, and the functionality has now been moved into the deinterlace element in gst-plugins-good as method=yadif (and LGPL).
See gst-plugins-good!444 (merged) and gst-plugins-good!621 (merged)
Closes #216 (closed) Fixes #463 (closed)