Move loading of mediawiki.toc from Parser to Skin
This was the only addModules() call ever to be inside Parser.
Introduced in a54ef1a203d. Prior to that, mediawiki.toc had always been loaded
by OutputPage (via mediawiki.util; and before that, via wikibits).
This patch restores that, and also fixes T130632 by making OutputPage get
it from the Skin, instead of hardcoding this somewhere in addParserOutput().
- Remove deprecated method OutputPage::enableTOC().
- Move mEnableTOC to addParserOutputText().