Update view testability attribute

The idea here is to use the new standard since qa- classes are now
deprecated.

Also, now the element name is more descriptive.

app/assets/javascripts/vue_shared/components/issue/related_issuable_item.vue

@@ -159,7 +159,8 @@ export default {
       v-gl-tooltip
       :disabled="removeDisabled"
       type="button"
-      class="btn btn-default btn-svg btn-item-remove js-issue-item-remove-button qa-remove-issue-button mr-xl-0 align-self-xl-center"
+      class="btn btn-default btn-svg btn-item-remove js-issue-item-remove-button mr-xl-0 align-self-xl-center"
+      data-qa-selector="remove_related_issue_button"
       :title="__('Remove')"
       :aria-label="__('Remove')"
       @click="onRemoveRequest"