* Remove 'wgMetaNamespace' and 'wgMetaNamespaceTalk', the same data
exists in 'wgFormattedNamespaces'.
* Rename 'wgContentLang' to 'wgContentLanguage', to match its real
name in JS config. MediaWiki doesn't use 'wgContentLang' anywhere,
although the related PHP global is called $wgContLang.
* Document how I made these files, previously only mentioned in the
commit message of e9c401e3aa.
Change-Id: I67f962812c155aedf41154e0d837e7feb5af972d