RN4W current needs to support newest CLI

[acoates-ms]

The current version of RN4W still uses the legacy rnpm plugin way of extending the react-native cli. This method has been deprecated for a while, but as of this PR it is no longer supported by the CLI.

I believe that this means that all the CLI commands (things like run-windows) will no longer work on the current version.

We are not investing in new features or lower priority bug fixes on the C# implementation of React Native for Windows (previously known as "vCurrent"). All investment moving forward is in the C++ infrastructure (previously known as "vNext") and that is the only option as of 0.61 (and was the default as of 0.60). If this issue is still relevant on the modern implementation please open a new issue. If this issue is of significant severity for a vCurrent app and vNext is not an option, re-open with justification.