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
startWorkTimer,
    stopWorkTimer,
    stopFailedWorkTimer,
    startWorkLoopTimer,
    stopWorkLoopTimer,
    startCommitTimer,
    stopCommitTimer,
    startCommitHostEffectsTimer,
    stopCommitHostEffectsTimer,
    startCommitLifeCyclesTimer,
    stopCommitLifeCyclesTimer,
  } = require('ReactDebugFiberPerf');
  var warnAboutUpdateOnUnmounted = function(
    instance: React$ComponentType<any>,
  ) {
    const ctor = instance.constructor;
    warning(
      false,
      'Can only update a mounted or mounting component. This usually means ' +
        'you called setState, replaceState, or forceUpdate on an unmounted ' +
        'component. This is a no-op.\n\nPlease check the code for the ' +
        '%s component.',
      (ctor && (ctor.displayName || ctor.name)) || 'ReactClass',
    );
  };
  var warnAboutInvalidUpdates = function(instance: React$ComponentType<any>) {
    switch (ReactDebugCurrentFiber.phase) {
      case 'getChildContext':
        warning(
          false,