Clean Up Helper/Uploader.php

[dmanners]

Preconditions (*)

1. 2.3-develop
2. PHPStan installed

Steps to reproduce (*)

1. Run ./vendor/bin/phpstan analyse app/code/Magento/DownloadableImportExport/Helper/Uploader.php

Expected result (*)

1. No Errors

Actual result (*)

 1/1 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%

 ------ --------------------------------------------------------------------------------------------------------------------------------
  Line   Uploader.php
 ------ --------------------------------------------------------------------------------------------------------------------------------
  63     Access to an undefined property Magento\DownloadableImportExport\Helper\Uploader::$connection.
 ------ --------------------------------------------------------------------------------------------------------------------------------


 [ERROR] Found 1 error