Fix Rx operators duplicated in net4 (#3085)

Co-authored-by: Chris Pulman <chris.pulman@yahoo.com>

Author: glennawatson

src/ReactiveUI.Tests/Platforms/winforms/API/WinformsApiApprovalTests.Winforms.Net4_8.verified.txt

@@ -106,12 +106,4 @@ namespace ReactiveUI.Winforms
         public int GetAffinityForObject(System.Type type, string propertyName, bool beforeChanged = false) { }
         public System.IObservable<ReactiveUI.IObservedChange<object, object?>> GetNotificationForProperty(object sender, System.Linq.Expressions.Expression expression, string propertyName, bool beforeChanged = false, bool suppressWarnings = false) { }
     }
-}
-namespace System.Reactive.Concurrency
-{
-    public class ControlScheduler : System.Reactive.Concurrency.LocalScheduler, System.Reactive.Concurrency.ISchedulerPeriodic { }
-}
-namespace System.Reactive.Linq
-{
-    public static class ControlObservable { }
 }

src/ReactiveUI.Winforms/ReactiveUI.Winforms.csproj

@@ -18,7 +18,7 @@
     <None Include="..\ReactiveUI.Uwp\Rx\**\*.cs" LinkBase="Rx" />
   </ItemGroup>
 
-  <ItemGroup Condition=" $(TargetFramework.StartsWith('net4')) or $(TargetFramework) == 'net6.0-windows' ">
+  <ItemGroup Condition=" $(TargetFramework) == 'net6.0-windows' ">
     <Compile Include="..\ReactiveUI.Uwp\Rx\Concurrency\ControlScheduler.cs" LinkBase="Rx" />
     <Compile Include="..\ReactiveUI.Uwp\Rx\Internal\Constants.cs" LinkBase="Rx" />
     <Compile Include="..\ReactiveUI.Uwp\Rx\Linq\**\*.cs" LinkBase="Rx" Exclude="..\ReactiveUI.Uwp\Rx\Linq\DispatcherObservable.cs" />

src/ReactiveUI.Wpf/ReactiveUI.Wpf.csproj

@@ -16,7 +16,7 @@
     <None Include="..\ReactiveUI.Uwp\Rx\**\*.cs" LinkBase="Rx" />
   </ItemGroup>
 
-  <ItemGroup Condition=" $(TargetFramework.StartsWith('net4')) or $(TargetFramework) == 'net6.0-windows' ">
+  <ItemGroup Condition=" $(TargetFramework) == 'net6.0-windows' or $(TargetFramework) == 'net462' ">
     <Compile Include="..\ReactiveUI.Uwp\Rx\Concurrency\DispatcherScheduler.cs" LinkBase="Rx" />
     <Compile Include="..\ReactiveUI.Uwp\Rx\Internal\Constants.cs" LinkBase="Rx" />
     <Compile Include="..\ReactiveUI.Uwp\Rx\Linq\**\*.cs" LinkBase="Rx" Exclude="..\ReactiveUI.Uwp\Rx\Linq\ControlObservable.cs" />