Fix expunging posts from S3 (fixup 4c4ef5c / #3180).

app/logical/backup_service.rb

@@ -2,4 +2,8 @@ class BackupService
   def backup(file_path, options = {})
     raise NotImplementedError.new("#{self.class}.backup not implemented")
   end
+
+  def delete(file_path, options = {})
+    raise NotImplementedError.new("#{self.class}.delete not implemented")
+  end
 end

app/logical/null_backup_service.rb

@@ -2,4 +2,8 @@ class NullBackupService
   def backup(file_path, options = {})
     # do nothing
   end
+
+  def delete(file_path, options = {})
+    # do nothing
+  end
 end

app/models/post.rb

@@ -74,6 +74,7 @@ class Post < ApplicationRecord
           end
         end
 
+        backup_service = Danbooru.config.backup_service
         backup_service.delete(file_path, type: :original)
         backup_service.delete(large_file_path, type: :large)
         backup_service.delete(preview_file_path, type: :preview)