Revert "Unset NUGET_PACKAGES in official build only (#9523)" (#9533)

This reverts commit 67d742f.
This workaround no more needed.

Author: AR-May

.vsts-dotnet.yml

@@ -94,8 +94,6 @@ stages:
       value: 'int.main'
     - name: VisualStudio.DropName
       value: Products/$(System.TeamProject)/$(Build.Repository.Name)/$(Build.SourceBranchName)/$(Build.BuildNumber)
-    - name: NUGET_PACKAGES
-      value:
 
     steps:
     - task: NuGetToolInstaller@0