Address review comments from @smcgivern.

1. Remove an unnecessary (since we're fetching all the records anyway)
   `pluck` while fetching U2F registration records.

2. Align "Your device was successfully set up!" section with the "U2F
   Devices" table below.

app/controllers/profiles/two_factor_auths_controller.rb

@@ -92,11 +92,10 @@ class Profiles::TwoFactorAuthsController < Profiles::ApplicationController
   def setup_u2f_registration
     @u2f_registration ||= U2fRegistration.new
     @u2f_registrations = current_user.u2f_registrations
-    @registration_key_handles = @u2f_registrations.pluck(:key_handle)
     u2f = U2F::U2F.new(u2f_app_id)
 
     registration_requests = u2f.registration_requests
-    sign_requests = u2f.authentication_requests(@registration_key_handles)
+    sign_requests = u2f.authentication_requests(@u2f_registrations.map(&:key_handle))
     session[:challenges] = registration_requests.map(&:challenge)
 
     gon.push(u2f: { challenges: session[:challenges], app_id: u2f_app_id,

app/views/u2f/_register.html.haml

@@ -28,6 +28,7 @@
 
 %script#js-register-u2f-registered{ type: "text/template" }
   %div.row.append-bottom-10
+    .col-md-12
       %p Your device was successfully set up! Give it a name and register it with the GitLab server.
       = form_tag(create_u2f_profile_two_factor_auth_path, method: :post) do
         .row.append-bottom-10