Remove RemoteAccountControllerConcern never used (#9482)

app/controllers/concerns/remote_account_controller_concern.rb

-# frozen_string_literal: true
-
-module RemoteAccountControllerConcern
-  extend ActiveSupport::Concern
-
-  included do
-    layout 'public'
-    before_action :set_account
-    before_action :check_account_suspension
-  end
-
-  private
-
-  def set_account
-    @account = Account.find_remote!(params[:acct])
-  end
-
-  def check_account_suspension
-    gone if @account.suspended?
-  end
-end