We don't actually use this anywhere, so let's remove it.

https://github.com/facebook/react/blob/f1d00156df5453bc62bd5668fefdcac4ca67e90e/src/renderers/shared/fiber/ReactFiberScheduler.js#L1504-L1512
var expect = require('jest-matchers');
const UPDATE_SIGNAL = {};
var scheduledCallback = null;
type Container = {rootID: string, children: Array<Instance | TextInstance>};
type Props = {prop: any, hidden?: boolean};
type Instance = {|
  type: string,
  id: number,
  children: Array<Instance | TextInstance>,
  prop: any,
|};
type TextInstance = {|text: string, id: number|};
var instanceCounter = 0;
var failInBeginPhase = false;
function appendChild(
  parentInstance: Instance | Container,
  child: Instance | TextInstance,
): void {
  const index = parentInstance.children.indexOf(child);
  if (index !== -1) {
    parentInstance.children.splice(index, 1);
  }
  parentInstance.children.push(child);
}
function insertBefore(
  parentInstance: Instance | Container,
  child: Instance | TextInstance,
  beforeChild: Instance | TextInstance,
): void {
  const index = parentInstance.children.indexOf(child);