Browser support: remove the "CSS contents and browser compatibility" link

[mgol]

The "CSS contents and browser compatibility" link from "External References" at the bottom of the page should be removed; it was mostly relevant for IE<8 and most of the table has since been moved to another place.

[mgol]

IMO the whole External References section could be dropped once we release jQuery 3.0. They're only relevant for IE<9 which we're dropping.