DVDFactoryCodec: Remove throttling of mpeg2 to libmpeg2 for amlogic

* Thanks to @kszaq, am-mpeg2 can handle all mpeg2's however it can't handle the still frames (which is caught above it).
* Testing .VOB isn't setting hint.stills to true so will need to address this in separate patch

Signed-off-by: Brandon McAnsh <brandonm@matricom.net>