login: remove login reminder page.

Remove the login reminder page. The meaning of "login reminder" wasn't
clear (it's for recovering a forgotten username) and the functionality
was redundant. The password reset page can already be used to recover
forgotten usernames.

There was also a privacy leak, since the login reminder page could be
used to find out whether a given email is in use on Danbooru.

config/routes.rb

@@ -59,7 +59,6 @@ Rails.application.routes.draw do
       resource :count_fixes, only: [:new, :create]
       resource :email_notification, :only => [:show, :destroy]
       resource :password_reset, :only => [:new, :create, :edit, :update]
-      resource :login_reminder, :only => [:new, :create]
       resource :deletion, :only => [:show, :destroy]
       resource :email_change, :only => [:new, :create]
       resource :dmail_filter, :only => [:edit, :update]