Revert to using Paperclip's filesystem storage, and fix dangling records in remove_remote (#8339)

* Fix uncaching worker

* Revert to using Paperclip's filesystem backend instead of fog-local

fog-local has lots of concurrency issues, causing failure to delete files,
dangling file records, and spurious errors UncacheMediaWorker

app/workers/maintenance/uncache_media_worker.rb

@@ -8,7 +8,7 @@ class Maintenance::UncacheMediaWorker
   def perform(media_attachment_id)
     media = MediaAttachment.find(media_attachment_id)
 
-    return unless media.file.exists?
+    return if media.file.blank?
 
     media.file.destroy
     media.save