Moved PackageOutputPath to NuGet's Pack targets (Fixes dotnet#10730)

This should free the SDK from having to manage NuGet Pack's `PackageOutputPath` property.
This was possible because of the `BaseOutputPath` that'll be used instead of `OutputPath` in the Pack targets.
It does depend on NuGet's Fix. Issue: NuGet/Home#9234 PR: NuGet/NuGet.Client#3270
Hopefully, this change won't break anything...

src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.DefaultOutputPaths.targets

@@ -40,10 +40,5 @@ Copyright (c) .NET Foundation. All rights reserved.
     <IntermediateOutputPath Condition=" $(IntermediateOutputPath) == '' and '$(PlatformName)' != 'AnyCPU' ">$(BaseIntermediateOutputPath)$(PlatformName)\$(Configuration)\</IntermediateOutputPath>
     <IntermediateOutputPath Condition="!HasTrailingSlash('$(IntermediateOutputPath)')">$(IntermediateOutputPath)\</IntermediateOutputPath>
   </PropertyGroup>
-
-  <!-- Set the package output path (for nuget pack target) now, before the TargetFramework is appended -->
-  <PropertyGroup>
-    <PackageOutputPath Condition="'$(PackageOutputPath)' == ''">$(OutputPath)</PackageOutputPath>
-  </PropertyGroup>
-
+
 </Project>