Revert "dvd/omxplayer: only change dvd sub visibility on user action"

This reverts commit 35665a24c6ef54a84e574edc1985926e219679cc.
dvdplayer: don't override video setting visibility if no subs are found

Note: This should be reverted when we have separated GUI display from
user specified settings.

It temporarily solves the use case of user starting a movie without subs,
stop it, add external subtitles, start it again.