User Guide: Drop-down menu for earlier versions doesn't work

The User Guide header contains a drop-down menu showing earlier versions of the manual, but the links don't work. Also, the drop-down for v1.1 doesn't have a link for the newer version, 1.2.
This is both a currently broken implementation and a future maintenance headache.
Since all (currently 3) versions are accessible from the Geode website's Docs page, let's just eliminate the version drop-down menu altogether.