[rbp] Don't override dvdplayer with omxplayer.

Using dvdplayer can be useful on the Pi. We can actually play sd (up to 640x480 MPEG-4 video) video in real time.
This is useful for codec variants like DivX3 which we don't currently play.

This may expose bugs where dvdplayer is incorrectly used as the default player which will need to be fixed