Revert "Fix viewdocs.phtml to accept two-letter or three-letter language codes"

This reverts commit bf0d3c3ce4c1b605707bc7934c71ce7300590810.
Makes the problem worse.
Revert "Fix the 2.6 documentation links for two-letter locale codes"

This reverts commit dbc305000cbabb45f36c684ca552d04da82c8af5.
Doesn't actually fix anything.