Remove dependabot NuGet config support. (#91)

* Sadly GitHub's dependabot configuration assumes
a very specific workflow can build the targets. But that's not possible in this repo. It requires use of the PoiweShell build scripts. There is no way I know of to configure the build actions for dependabot support. It's basically borked with far too limited functionality to be useable in this real-world case.

Author: smaillet