Remove unnecessary margin to the right of the Show comment only dropdown

There was unnecessary margin beside the Show comment only dropdown in Merge Request view. Remove the gl-mr-3 class which will remove the space beside the dropdown.

Changelog: fixed

app/assets/javascripts/notes/components/discussion_filter.vue

@@ -116,7 +116,7 @@ export default {
   <gl-dropdown
     v-if="displayFilters"
     id="discussion-filter-dropdown"
-    class="gl-mr-3 full-width-mobile discussion-filter-container js-discussion-filter-container"
+    class="full-width-mobile discussion-filter-container js-discussion-filter-container"
     data-qa-selector="discussion_filter_dropdown"
     :text="currentFilter.title"
     :disabled="isLoading"