Delete empty folders in clean operation up to the start destination folder.

[YangLyu89]

Minimal repro steps

1. Have a libman.json file with the content like
   {
   "version": "1.0",
   "defaultProvider": "cdnjs",
   "libraries": [
   {
   "destination": "wwwroot/lib/jquery/",
   "library": "jquery@3.3.1"
   }
   ]
   }
2. Restore client-side libraries
3. Clean client-side libraries

The wwwroot folder will be deleted

We can probably keep a record of the wwwroot folder here. Or if starting on UI by right click on wwwroot, and adding client-side library, do the same. So we can remain the wwwroot empty folder.

[jodavis]

We're not sure if this change in behavior is necessary.