Remove old reference to inst._wrapperState (#12987)

This commit removes a reference to inst._wrapperState, which was the
old way of tracking input state in the stack renderer.

This means we no longer need to pass the instance into the associated
function, allowing us to eliminate an exception for IE (and a TODO).

Author: nhunzaker

packages/react-dom/src/events/ChangeEventPlugin.js

@@ -231,14 +231,8 @@ function getTargetInstForInputOrChangeEvent(topLevelType, targetInst) {
   }
 }
 
-function handleControlledInputBlur(inst, node) {
-  // TODO: In IE, inst is occasionally null. Why?
-  if (inst == null) {
-    return;
-  }
-
-  // Fiber and ReactDOM keep wrapper state in separate places
-  let state = inst._wrapperState || node._wrapperState;
+function handleControlledInputBlur(node) {
+  let state = node._wrapperState;
 
   if (!state || !state.controlled || node.type !== 'number') {
     return;
@@ -303,7 +297,7 @@ const ChangeEventPlugin = {
 
     // When blurring, set the value attribute for number inputs
     if (topLevelType === TOP_BLUR) {
-      handleControlledInputBlur(targetInst, targetNode);
+      handleControlledInputBlur(targetNode);
     }
   },
 };