Remove leftover database columns from Devise::Models::Rememberable (#17191)

* Remove leftover database columns from Devise::Models::Rememberable

* Update fix-duplication maintenance script

* Improve errors/warnings in the fix-duplicates maintenance script

db/post_migrate/20220118183010_remove_index_users_on_remember_token.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+class RemoveIndexUsersOnRememberToken < ActiveRecord::Migration[6.1]
+  disable_ddl_transaction!
+
+  def up
+    remove_index :users, name: :index_users_on_remember_token
+  end
+
+  def down
+    add_index :users, :remember_token, algorithm: :concurrently, unique: true, name: :index_users_on_remember_token
+  end
+end

db/post_migrate/20220118183123_remove_rememberable_from_users.rb

@@ -0,0 +1,8 @@
+class RemoveRememberableFromUsers < ActiveRecord::Migration[6.1]
+  def change
+    safety_assured do
+      remove_column :users, :remember_token, :string, null: true, default: nil
+      remove_column :users, :remember_created_at, :datetime, null: true, default: nil
+    end
+  end
+end