Don't manage the ChocolateyInstall path

Either due to 7cdd777f8bc0661fbf8d58110562c910b07b8c53 or because of the radical changes in Chocolatey 0.9.21+ we no longer need to manually set the *ChocolateyInstall* environment variable.

This includes a basic *chocopacks.bat* so our friends don't have to waste hours figuring it out on their own.