omxvideodec: remove dead code
omxvideodec: remove dead code

This code doesn't seems to be used for quite a while,
remove it before it starts to rot.

https://bugzilla.gnome.org/show_bug.cgi?id=724236

freedesktop-unofficial-mirror/gstreamer__gst-omx,surround-io/gst-omx,freedesktop-unofficial-mirror/gstreamer__gst-omx,GStreamer/gst-omx,varunkumara/test-repo,CapOM/gst-omx,varunkumara/test-repo,GStreamer/gst-omx,pliu6/gst-omx,surround-io/gst-omx,renesas-rcar/gst-omx,varunkumara/test-repo,CapOM/gst-omx,CapOM/gst-omx,leio/gst-omx,GStreamer/gst-omx,ismelykh/gst-omx-deinterlace,leio/gst-omx,renesas-rcar/gst-omx,renesas-rcar/gst-omx,ismelykh/gst-omx-deinterlace,pliu6/gst-omx