Revert "[Fix][DVD/OMXPlayer] This fixes a regression introduced in 50a1d3c."

This reverts commits bb1aeb75e13adc0bdb6befb69feca44997e5552b and fdacd42bcebc4197c75a24c6ea54511b796b396e.

The fix is invalid and causes a mismatch between GUI assumed subtitle
and what the player actually is playing.
dvd/omxplayer: add internal version of SetSubtitleVisible

This avoids overriding result of OpenDefaultStreams forced/relevant
calculation due to SetSubtitleVisible being delayed by message
queue.

Original-patch-by: ace20022 <ace20022@xbmc.org>
dvd/omxplayer Subs couldn't be turned on if no relevant subs existed

Original patch by: ace20022
dvd/omxplayer: 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.
Merge pull request #4176 from elupus/sub_fixes

Sub fixes