Replace Makara with an initial Rails 6 role based splitting method.

app/models/backup.rb

@@ -7,7 +7,7 @@
 #  user_id           :bigint(8)
 #  dump_file_name    :string
 #  dump_content_type :string
-#  dump_file_size    :bigint(8)
+#  dump_file_size    :integer
 #  dump_updated_at   :datetime
 #  processed         :boolean          default(FALSE), not null
 #  created_at        :datetime         not null