VideoCommon{Backends}: Remove unnecessary wxWidgets references.

Also EmuWindow doesn't even exist anymore.

Turns out InputCommon actually relied on wx linking in the correct OSX libraries, so it removes even more coupling in that regard.

Now building VideoCommon and the Software and OGL backends isn't blocked by the compilation of wx (at least on OSX. *nix just ignores building the static version if wx is already installed on the system).