Unfortunately this file cannot be removed yet. StyleCop is not packaged as a build target package using the `build` NuGet folder. Build target packages were only supported from NuGet 2.6 onwards and package restore for build target packages only started working properly from NuGet 2.7 onwards. StyleCop.MSBuild pre-dates 2.7 considerably. NuGet 2.7 adoption seems to be quite wide now so I will probably convert StyleCop.MSBuild to using the `build` folder some time this month, but until then this file has to be added to source control. This can be done using the weird incantations found in the `.gitignore` for ConfigR (https://github.com/config-r/config-r/blob/dev/.gitignore#L9).