update dependencies in C# examples to GA versions

examples/csharp/.nuget/packages.config

examples/csharp/helloworld-from-cli/Greeter/project.json

...les/csharp/helloworld-from-cli/GreeterClient/project.json

...les/csharp/helloworld-from-cli/GreeterServer/project.json

examples/csharp/helloworld/Greeter/Greeter.csproj

examples/csharp/helloworld/Greeter/packages.config

...ples/csharp/helloworld/GreeterClient/GreeterClient.csproj

examples/csharp/helloworld/GreeterClient/packages.config

...ples/csharp/helloworld/GreeterServer/GreeterServer.csproj

examples/csharp/helloworld/GreeterServer/packages.config

examples/csharp/helloworld/generate_protos.bat

examples/csharp/route_guide/RouteGuide/RouteGuide.csproj

examples/csharp/route_guide/RouteGuide/packages.config

...harp/route_guide/RouteGuideClient/RouteGuideClient.csproj

examples/csharp/route_guide/RouteGuideClient/packages.config

...harp/route_guide/RouteGuideServer/RouteGuideServer.csproj

examples/csharp/route_guide/RouteGuideServer/packages.config

examples/csharp/route_guide/generate_protos.bat