Remove dead code 🚮 (#3023)

Author: benrr101

src/Microsoft.Data.SqlClient/netfx/src/Microsoft.Data.SqlClient.csproj

@@ -812,7 +812,6 @@
     <Compile Include="Microsoft\Data\Interop\SNINativeManagedWrapperX64.cs" />
     <Compile Include="Microsoft\Data\Interop\SNINativeManagedWrapperX86.cs" />
     <Compile Include="Microsoft\Data\Interop\SNINativeMethodWrapper.cs" />
-    <Compile Include="Microsoft\Data\RelationshipConverter.cs" />
     <Compile Include="Microsoft\Data\SqlClient\assemblycache.cs" />
     <Compile Include="Microsoft\Data\SqlClient\LocalDBAPI.cs" />
     <Compile Include="Microsoft\Data\SqlClient\LocalDBConfig.cs" />