Remove GenericEnumerator class as it is obsolete/unused (#9862)

Author: h3xds1nz

src/Microsoft.DotNet.Wpf/src/PresentationCore/PresentationCore.csproj

@@ -47,7 +47,6 @@
     <Compile Include="$(WpfSharedDir)\MS\Internal\FreezableOperations.cs" />
     <Compile Include="$(WpfSharedDir)\MS\Internal\HashHelper.cs" />
     <Compile Include="$(WpfSharedDir)\MS\Internal\PointUtil.cs" />
-    <Compile Include="$(WpfSharedDir)\MS\Internal\GenericEnumerator.cs" />
     <Compile Include="$(WpfSharedDir)\MS\Internal\MimeTypeMapper.cs" />
     <Compile Include="$(WpfSharedDir)\MS\Internal\Pair.cs" />
     <Compile Include="$(WpfSharedDir)\MS\Internal\PartialList.cs" />