Retire legacy Lua API and IRC code.

Our new Lua API has now grown up enough to supersede the old API.  The IRC code hasn't seen any work in the last year, and it may make sense to delegate this responsibility to a thirdparty library such as [SmartIrc4net](https://github.com/meebey/SmartIrc4net) if somebody wants to resume work on the global chat.

Test packages: [OSX](http://build.openra.net/removetest/OpenRA-test-20141019.zip), [Windows](http://build.openra.net/removetest/OpenRA-test-20141019.exe), [deb](http://build.openra.net/removetest/openra_test.20141019_all.deb), [rpm](http://build.openra.net/removetest/openra-test.20141019-1.noarch.rpm), [pkgbuild](http://build.openra.net/removetest/openra-test.20141019-1-any.pkg.tar.xz).