Admission-based registrations mode (#10250)

Fix #6856
Fix #6951

app/views/layouts/public.html.haml

@@ -10,8 +10,7 @@
             = link_to root_url, class: 'brand' do
               = image_tag asset_pack_path('logo_full.svg'), alt: 'Mastodon'
 
-            - if Setting.profile_directory
-              = link_to t('directories.directory'), explore_path, class: 'nav-link optional'
+            = link_to t('directories.directory'), explore_path, class: 'nav-link optional' if Setting.profile_directory
             = link_to t('about.about_this'), about_more_path, class: 'nav-link optional'
             = link_to t('about.apps'), 'https://joinmastodon.org/apps', class: 'nav-link optional'
           .nav-center
@@ -20,7 +19,7 @@
               = link_to t('settings.back'), root_url, class: 'nav-link nav-button webapp-btn'
             - else
               = link_to t('auth.login'), new_user_session_path, class: 'webapp-btn nav-link nav-button'
-              = link_to t('auth.register'), open_registrations? ? new_user_registration_path : 'https://joinmastodon.org/#getting-started', class: 'webapp-btn nav-link nav-button'
+              = link_to t('auth.register'), available_sign_up_path, class: 'webapp-btn nav-link nav-button'
 
     .container= yield