Merge pull request #176 from openHPI/fix/destroy-files-from-exercise-edit

fix deleting files from exercise edit

app/views/exercises/_file_form.html.slim

@@ -7,7 +7,9 @@ li.panel.panel-default
         span = f.object.name
   .panel-collapse.collapse class=('in' if f.object.name.nil?) id="collapse#{id}" role="tabpanel"
     .panel-body
-      .clearfix = link_to(t('shared.destroy'), '#', class:'btn btn-warning btn-sm discard-file pull-right')
+      - if policy(f.object).destroy?
+        .clearfix
+          .btn.btn-warning.btn-sm.pull-right.delete-file data-file-url=code_ocean_file_path(id) = t('shared.destroy')
       .form-group
         = f.label(:name, t('activerecord.attributes.file.name'))
         = f.text_field(:name, class: 'form-control')
@@ -37,4 +39,4 @@ li.panel.panel-default
         .form-group
           = f.label(:role, t('activerecord.attributes.file.weight'))
           = f.number_field(:weight, class: 'form-control', min: 1, step: 'any')
-      = render('code_field', attribute: :content, form: f, label: t('activerecord.attributes.file.content'))
+      = render('code_field', attribute: :content, form: f, label: t('activerecord.attributes.file.content'))