Remove nuspecs as no longer needed

[jchannon]

Prerequisites

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• I have provided test coverage for my change (where applicable)

Description

We use project.json now so *nuspecs are no longer required

[jvandertil]

Seems like a good change, I'm assuming this is also the case with the new csproj format?

[thecodejunkie]

@jvandertil Our build scripts use dotnet pack to build all NuGet packages these days, so the *.nuspec files aren't really used anymore. Once Visual Studio 2017 gets closer to RTM then we will have a look at how we will support the new csproj-format. It's not all black and white, I am afraid, since from what I have gathered they will not back port the tooling to Visual Studio 2015 and we will have to assume that for a while that's what most of our users will continue to support. Of course we want to move over to the new csproj format so with a bit of luck we can support both scenarios without too much hassle (supporting csproj and project.json today was a major PITA because of the tooling support)