regenerate C# protos

src/csharp/Grpc.Examples/Math.cs

src/csharp/Grpc.Examples/MathGrpc.cs

src/csharp/Grpc.HealthCheck/Health.cs

src/csharp/Grpc.HealthCheck/HealthGrpc.cs

src/csharp/Grpc.IntegrationTesting/Control.cs

src/csharp/Grpc.IntegrationTesting/Empty.cs

src/csharp/Grpc.IntegrationTesting/Messages.cs

src/csharp/Grpc.IntegrationTesting/Metrics.cs

src/csharp/Grpc.IntegrationTesting/MetricsGrpc.cs

src/csharp/Grpc.IntegrationTesting/Payloads.cs

src/csharp/Grpc.IntegrationTesting/Services.cs

src/csharp/Grpc.IntegrationTesting/ServicesGrpc.cs

src/csharp/Grpc.IntegrationTesting/Stats.cs

src/csharp/Grpc.IntegrationTesting/Test.cs

src/csharp/Grpc.IntegrationTesting/TestGrpc.cs