replacements: don't delete replaced files.

Don't delete replaced files after 30 days. There are only about 30k
replacements in total, so the cost of keeping replaced files is
negligible. It was also wrong because the media asset wasn't destroyed
too, so there were active media assets with missing files.

app/jobs/delete_post_files_job.rb

@@ -1,10 +0,0 @@
-# A job that deletes a post's files after it's replaced, or a preprocessed
-# upload is never completed.
-class DeletePostFilesJob < ApplicationJob
-  queue_as :default
-  queue_with_priority 20
-
-  def perform(id, md5, file_ext)
-    Post.delete_files(id, md5, file_ext)
-  end
-end

app/logical/upload_service/replacer.rb

@@ -79,7 +79,6 @@ class UploadService
       end
 
       media_asset = MediaAsset.upload!(media_file)
-      post.queue_delete_files(PostReplacement::DELETION_GRACE_PERIOD)
 
       replacement.replacement_url = replacement_url
       replacement.file_ext = media_asset.file_ext

app/models/post.rb

@@ -91,10 +91,6 @@ class Post < ApplicationRecord
       end
     end
 
-    def queue_delete_files(grace_period)
-      DeletePostFilesJob.set(wait: grace_period).perform_later(id, md5, file_ext)
-    end
-
     def delete_files
       Post.delete_files(id, md5, file_ext, force: true)
     end

app/models/post_replacement.rb

@@ -1,6 +1,4 @@
 class PostReplacement < ApplicationRecord
-  DELETION_GRACE_PERIOD = 30.days
-
   belongs_to :post
   belongs_to :creator, class_name: "User"
   before_validation :initialize_fields, on: :create