Change older Paperclip database migrations for consistency (#30204)

db/migrate/20170917153509_create_custom_emojis.rb

@@ -5,7 +5,12 @@ class CreateCustomEmojis < ActiveRecord::Migration[5.1]
     create_table :custom_emojis do |t|
       t.string :shortcode, null: false, default: ''
       t.string :domain
-      t.attachment :image
+
+      # The following corresponds to `t.attachment :image` in an older version of Paperclip
+      t.string :image_file_name
+      t.string :image_content_type
+      t.integer :image_file_size
+      t.datetime :image_updated_at
 
       t.timestamps
     end