Hide sign up link in mobile header when registrations are disabled

closes #8060

Changelog.md

@@ -6,6 +6,7 @@
 
 ## Bug fixes
 * Fix error while trying to fetch some sites with invalid OpenGraph data [#8049](https://github.com/diaspora/diaspora/pull/8049)
+* Don't show sign up link on mobile when registrations are disabled [#8060](https://github.com/diaspora/diaspora/pull/8060)
 
 ## Features
 * Add cronjob to cleanup pending photos which were never posted [#8041](https://github.com/diaspora/diaspora/pull/8041)

app/helpers/sessions_helper.rb

@@ -11,7 +11,7 @@ module SessionsHelper
   end
 
   def display_registration_link?
-    AppConfig.settings.enable_registrations? && devise_mapping.registerable? && controller_name != "registrations"
+    AppConfig.settings.enable_registrations? && controller_name != "registrations"
   end
 
   def display_password_reset_link?

app/views/layouts/_header_not_connected.haml

@@ -1,5 +1,5 @@
 %ul.nav.navbar-nav.navbar-right
-  - unless current_page?(controller: "/registrations", action: :new)
+  - if display_registration_link? && !current_page?(controller: "/registrations", action: :new)
     %li= link_to t("devise.shared.links.sign_up"), new_user_registration_path, class: "login"
   - unless current_page?(controller: "/sessions", action: :new)
     %li= link_to t("devise.shared.links.sign_in"), new_user_session_path, class: "login"