Remove legacy "check" and "repair" functionality in package-release-nodes.php

Back when the "new" release system was new, I had to add code to our packaging script to verify (and at times repair) the file metadata associated with release nodes. None of this code works now that release nodes can have multiple files per release, and none of it's been used in years. In the spirit of #1019354: Remove packaging script support for translations and to further make life easier for #781246: Write Git-specific packaging plugin for d.o I'm going to rip out all this code, too.