(see bug 29712) Removing the defaultUserOptionOverrides in MessagesXx.php because...

(see bug 29712) Removing the defaultUserOptionOverrides in MessagesXx.php because it is broken (and has been for a long time) and secondly, it is only used for things that can be done otherwise:
* 'editfont' => 'sans-serif'; -> trivial (can be set in CSS)
* 'underline' => 0; by languages written in scripts that are hard to read with underlines -> now set in shared.css, which makes it work also when they are used as interface language (note that [lang="xx"] is not yet present on wikitext content by default but will be soon as part of my work on RTL improvements)
* 'quickbar' => 2; by RTL languages. For this, I introduced a new option (5) that sets left/right according to the directionality of your interface language (and automatic is better than setting it in MessagesXx files!). Note that the broken feature was in this case "corrected" by CSS flipping, causing preferences to say "left" while it was actually "right". This commit fixes that bug as well.
Third, it actually would have made more sense to have it them load for wgLang instead of wgContLang, but that's not possible because wgLang is itself dependent on preferences