changed: Remove display of XBOX dvd icon unused code

This would display a XBOX dvd icon if DefaultXboxDVD.png still existed
which doesnt anymore,
change: remove unused xbox overlay support

This is legacy from the xbox days. highly unlikely to ever be used again

ICON_OVERLAY_TRAINED
ICON_OVERLAY_HAS_TRAINER

and removes references to respective unused textures

OverlayTrained.png
OverlayHasTrainer.png
Merge pull request #4909 from uNiversaI/xbox-cleanup

[Cleanup] Remove some old unused Xbox references and code.