Use each loop because index is no longer used

See
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12372#note_34120330

app/views/projects/pipeline_schedules/_form.html.haml

@@ -27,8 +27,7 @@
       %label.label-light
         #{ _('Variables') }
       %ul.js-pipeline-variable-list.pipeline-variable-list
-        - if @schedule.variables.present?
-          - @schedule.variables.each_with_index do |variable, i|
+        - @schedule.variables.each do |variable|
           = render 'variable_row', id: variable.id, key: variable.key, value: variable.value
         = render 'variable_row'
   .form-group