Revert "THRIFT-3000 .NET implementation has trouble with mixed IP modes"

This reverts commit 018c1b8f77e7d69da61014437d5f04fedbaad81d.
diff --git a/lib/csharp/src/Thrift.csproj b/lib/csharp/src/Thrift.csproj
index dc0aa6d..195005a 100644
--- a/lib/csharp/src/Thrift.csproj
+++ b/lib/csharp/src/Thrift.csproj
@@ -27,7 +27,7 @@
     <OutputType>Library</OutputType>
     <NoStandardLibraries>false</NoStandardLibraries>
     <AssemblyName>Thrift</AssemblyName>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v3.5</TargetFrameworkVersion>
     <FileAlignment>512</FileAlignment>
     <RootNamespace>Thrift</RootNamespace>
     <FileUpgradeFlags>
@@ -109,7 +109,6 @@
     <Compile Include="TException.cs" />
     <Compile Include="TApplicationException.cs" />
     <Compile Include="TProcessor.cs" />
-    <Compile Include="Transport\TSocketVersionizer.cs" />
     <Compile Include="Transport\TBufferedTransport.cs" />
     <Compile Include="Transport\TFramedTransport.cs" />
     <Compile Include="Transport\THttpClient.cs" />
@@ -148,4 +147,4 @@
   <ProjectExtensions>
     <VisualStudio AllowExistingFolder="true" />
   </ProjectExtensions>
-</Project>
\ No newline at end of file
+</Project>