Downloads directory is not deleted after running `gvfs upgrade` and subsequent non-elevated `gvfs upgrade` commands report an error

1. Upgrade VFS4G via gvfs upgrade --confirm
2. Open a non-elevated CMD prompt and run gvfs upgrade
3. The follow error is logged and reported via telemetry:

[2019-02-22 13:38:23 -08:00] Error {"ErrorMessage":"DeleteAllInstallerDownloads: Could not remove directory: C:\ProgramData\GVFS\GVFS.Upgrade\Downloads.System.ArgumentException: Access to the path is denied.\r\n at System.IO.FileSystemInfo.set_Attributes(FileAttributes value)\r\n at GVFS.Common.FileSystem.PhysicalFileSystem.RecursiveDelete(String path)\r\n at GVFS.Common.ProductUpgraderInfo.DeleteAllInstallerDownloads()"}

Two issues here:

• The downloads directory should have been deleted after the upgrade
• gvfs upgrade should not report an error if DeleteAllInstallerDownloads fails when running non-elevated (in fact it should probably not try to delete the directory at all).