MathJax Localization: Remove language menu

This way the cookie is never set and MathJax simply always follows
the MediaWiki language.

Follow up of Ibf43a3e44ea2bfdbd9fddc01c71c72ba097ff1b7
Bug: 35038

Change-Id: Ie7530d3a904fb39945ba8b8d261852c2b8cb666b