Remove stale property (#51615)

The by the SDK default included netframework reference assembly are used instead of the old microsoft.netframework.targetingpack. Removing the stale property.

src/libraries/System.Net.Http.WinHttpHandler/src/System.Net.Http.WinHttpHandler.csproj

@@ -8,8 +8,6 @@
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
     <GeneratePlatformNotSupportedAssemblyMessage Condition="$(TargetFramework.StartsWith('netstandard')) and '$(TargetsWindows)' != 'true'">SR.PlatformNotSupported_WinHttpHandler</GeneratePlatformNotSupportedAssemblyMessage>
-    <!-- Ensure Assemblies are first resolved via targeting pack when targeting net461 -->
-    <AssemblySearchPaths Condition="'$(TargetFramework)' == 'net461'">$(NuGetPackageRoot)\microsoft.targetingpack.netframework.v4.6.1\1.0.1\lib\net461\;$(AssemblySearchPaths)</AssemblySearchPaths>
   </PropertyGroup>
   <ItemGroup Condition="$([MSBuild]::GetTargetFrameworkIdentifier('$(TargetFramework)')) != '.NETCoreApp'">
     <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\UnconditionalSuppressMessageAttribute.cs" />