Eliminate Microsoft.Build.Locator source-build prebuilt

During source-build the following package is being reported as a prebuilt in 7.0.2xx.

```

```

This package is produced as part of the source-build graph but not version 1.5.5. To fix this, dotnet-format should utilizing a versions.props property to define the version number so that it can be overridden by source-build to the version it builds. In other words use the pattern used to define the Microsoft.Build version.