Merge pull request #1533 from jtattermusch/csharp_cleanup

src/csharp/Grpc.Auth/GoogleCredential.cs

src/csharp/Grpc.Auth/Grpc.Auth.csproj

src/csharp/Grpc.Auth/packages.config

src/csharp/Grpc.Examples.Tests/Grpc.Examples.Tests.csproj

src/csharp/Grpc.Examples.Tests/MathClientServerTests.cs

src/csharp/Grpc.Examples.Tests/packages.config

src/csharp/Grpc.Examples/Grpc.Examples.csproj

src/csharp/Grpc.Examples/MathExamples.cs

src/csharp/Grpc.Examples/MathServiceImpl.cs

src/csharp/Grpc.Examples/packages.config