Remove syntax help link and update screenshot

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9219#note_23943262

app/views/admin/application_settings/_form.html.haml

@@ -221,8 +221,6 @@
         .help-block
           Set the default expiration time for each job's artifacts.
           0 for unlimited.
-          = surround '(', ')' do
-            = link_to 'syntax', help_page_path('ci/yaml/README', anchor: 'artifactsexpire_in')
           = link_to icon('question-circle'), help_page_path('user/admin_area/settings/continuous_integration', anchor: 'default-artifacts-expiration')
 
   - if Gitlab.config.registry.enabled