Revert "Move update scheduling to microtask (#26512)"

This reverts commit 09c8d25.

Author: kassens

packages/react-devtools-shared/src/__tests__/profilingCache-test.js

@@ -963,7 +963,7 @@ describe('ProfilingCache', () => {
             2 => 0,
           },
           "passiveEffectDuration": null,
-          "priorityLevel": "Normal",
+          "priorityLevel": "Immediate",
           "timestamp": 0,
           "updaters": [
             {

packages/react-reconciler/src/ReactFiberRoot.js

@@ -63,7 +63,6 @@ function FiberRootNode(
   this.cancelPendingCommit = null;
   this.context = null;
   this.pendingContext = null;
-  this.next = null;
   this.callbackNode = null;
   this.callbackPriority = NoLane;
   this.eventTimes = createLaneMap(NoLanes);