Rename this tool to `dotnet-uninstall`

The "Core" branding is long gone from the .NET ecosystem. No supported versions of .NET use "Core" anymore (see https://dotnet.microsoft.com/en-us/download/dotnet).

I think it is time to drop the `core` part of the name of this tool.

This very minor change would make the .NET ecosystem slightly more user friendly to newcomers, i.e. only 2 CLI tools are needed (`dotnet` and `dotnet-uninstall`) – and they have similar names.