chore(x11/mpv): make X11 default backend

[twaik]

By default mpv chooses wrong video backend and shows this:

Error opening/initializing the selected video_out (--vo) device.
Video: no video

This patch fixes it.

I will merge it in 72 hours if no one minds. Or anyone else can merge it earlier.

[TomJo2000]

Patching it is definitely the better approach but we could also set a default using the mpv.conf

[twaik]

This change may break user's setup. I mean you seen these annoying apt prompts where it asks you if you want to obtain vendor's version of config or keep your version, right?

[twaik]

Also anyway mediacodec backend requires JNI so it is useless...

[TomJo2000]

Yeah patching is definitely the better solution here.