Remove padding for mr-widget-section

This class is used in:

- `group_test_reports_app.vue` where the padding is overruled by
  `.mr-report`
- `mr_widget_options.vue` where the padding is overruled by `p-0`
- `ee/mr_widget_options.vue` where there is a bug because the padding
  is not overruled.

app/assets/javascripts/vue_merge_request_widget/mr_widget_options.vue

@@ -315,7 +315,7 @@ export default {
         :endpoint="mr.testResultsPath"
       />
-      <div class="mr-widget-section p-0">
+      <div class="mr-widget-section">
         <component :is="componentName" :mr="mr" :service="service" />
         <section v-if="shouldRenderCollaborationStatus" class="mr-info-list mr-links">

app/assets/stylesheets/pages/merge_requests.scss

@@ -82,7 +82,6 @@
 }
 .mr-widget-body,
-.mr-widget-section,
 .mr-widget-content,
 .mr-widget-footer {
   padding: $gl-padding;