jakeboy kindly explained his solution to me. He found a simple and reversible way to uninstall "DVD Player". So his solution relies on shifting to VLC player (or another non-Apple player).
VLC is a good versatile player. It plays very many formats. For example, it plays my self-made blu-rays. But kurt188, posting in February 2012, made the point that Apple's "DVD Player" might be a superior DVD player. I've found "DVD Player" to have unusual playback qualities, and posted about this in a video editing forum: http://www.lafcpug.org/phorum/read.php?1,277198,279613#msg-279613. "DVD Player" can deinterlace with high accuracy: 50i can look like 50p. It would be a pity to dump "DVD Player" because of the DVD region code problem.