moved interop testing specific files to Grpc.IntegrationTesting

src/csharp/Grpc.Api/Grpc.Api.csproj

@@ -53,9 +53,6 @@
     <Compile Include="Math.cs" />
     <Compile Include="MathGrpc.cs" />
     <Compile Include="MathServiceImpl.cs" />
-    <Compile Include="Empty.cs" />
-    <Compile Include="Messages.cs" />
-    <Compile Include="TestServiceGrpc.cs" />
     <Compile Include="MathExamples.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />

src/csharp/Grpc.IntegrationTesting/Grpc.IntegrationTesting.csproj

@@ -44,6 +44,9 @@
   <ItemGroup>
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="Client.cs" />
+    <Compile Include="TestServiceGrpc.cs" />
+    <Compile Include="Empty.cs" />
+    <Compile Include="Messages.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <ItemGroup>

src/csharp/Grpc.IntegrationTesting/TestServiceGrpc.cs

@@ -33,7 +33,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Reactive.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using Grpc.Core;