Hooray, I'm so glad! Enjoy!!
You can totally delete the installer, that shouldn't be an issue. Uninstalling Visual Studio itself should be okay too if you want to do that. I'm not sure if my speculation about breaking changes in Windows is correct or if the Visual Studio installer installed a needed dependency; if it is a dependency issue, uninstalling Visual Studio might remove that dependency, although I would be kind of surprised. If you uninstall Visual Studio and the game stops working, I would suggest installing the latest Microsoft Visual C++ Redistributable for your architecture, which is currently this one in your case. I think it should just stick around if Visual Studio installed it, though.
Also, in case it was a matter of breaking changes in Windows, it would be lovely if you'd be willing to email me the version of `GetFileSize.dll` you built. That way, if anyone else has this problem and it does seem to be an issue with recent versions of Windows, I can provide them with that version of the library.