Revert "Fix OpenID spec failure that assumed current_sign_in_at would be set"

This reverts commit 73f448e5.

spec/requests/openid_connect_spec.rb

 require 'spec_helper'
 
 describe 'OpenID Connect requests' do
-  let(:user) { create(:user, current_sign_in_at: Time.now) }
+  let(:user) { create :user }
   let(:access_grant) { create :oauth_access_grant, application: application, resource_owner_id: user.id }
   let(:access_token) { create :oauth_access_token, application: application, resource_owner_id: user.id }