Replace append-right-15 css class

This replaces the append-right-15 css
class for the gl-mr-5 utility class
from GitLab-UI

app/assets/javascripts/ci_variable_list/components/ci_variable_modal.vue

@@ -242,7 +242,7 @@ export default {
         <gl-form-group
           :label="__('Type')"
           label-for="ci-variable-type"
-          class="w-50 append-right-15"
+          class="w-50 gl-mr-5"
           :class="{ 'w-100': isGroup }"
         >
           <gl-form-select id="ci-variable-type" v-model="variable_type" :options="typeOptions" />

app/assets/stylesheets/framework/common.scss

@@ -402,7 +402,6 @@ img.emoji {
 .prepend-left-15 { margin-left: 15px; }
 .prepend-left-20 { margin-left: 20px; }
 .prepend-left-64 { margin-left: 64px; }
-.append-right-15 { margin-right: 15px; }
 .append-right-20 { margin-right: 20px; }
 .append-bottom-10 { margin-bottom: 10px; }
 .append-bottom-20 { margin-bottom: 20px; }