fixup! Import System.Windows.Forms global usings

Author: RussKie

eng/WindowsForms.targets

@@ -11,9 +11,6 @@
     <ItemGroup>
       <_WinFormsContent Include="$(_WinFormsContentPath)" />
     </ItemGroup>
-
-    <Error Text="Microsoft.Private.Winforms NuGet package contains no content. Is this expected?"
-           Condition="@(_WinFormsContent->Count()) == 0"/>
   </Target>
 
 </Project>

packaging/Microsoft.NET.Sdk.WindowsDesktop/targets/Microsoft.NET.Sdk.WindowsDesktop.props

@@ -161,6 +161,11 @@
     <SupportedTargetFramework Remove="@(_UnsupportedNETCoreAppTargetFramework);@(_UnsupportedNETStandardTargetFramework);@(_UnsupportedNETFrameworkTargetFramework)" />
   </ItemGroup>
 
-  <Import Project="System.Windows.Forms.GlobalUsings.props" />
+  <!--
+    Import Windows Forms props.
+    These come via the Windows Forms transport package, that can be found under
+    https://github.com/dotnet/winforms/tree/main/pkg/Microsoft.Private.Winforms/sdk
+  -->
+  <Import Project="System.Windows.Forms.props" />
 
 </Project>

packaging/Microsoft.NET.Sdk.WindowsDesktop/targets/Microsoft.NET.Sdk.WindowsDesktop.targets

@@ -155,6 +155,11 @@
   <!-- Import WPF Build logic only when we don't import NETFX's WinFX targets -->
   <Import Project="Microsoft.WinFX.targets" Condition="'$(ImportFrameworkWinFXTargets)' != 'true'"/>
 
-  <Import Project="System.Windows.Forms.GlobalUsings.targets" />
+  <!--
+    Import Windows Forms targets.
+    These come via the Windows Forms transport package, that can be found under
+    https://github.com/dotnet/winforms/tree/main/pkg/Microsoft.Private.Winforms/sdk
+  -->
+  <Import Project="System.Windows.Forms.targets" />
 
 </Project>