Remove TimerMixin on ReactContentSizeUpdateTest (#21502)

Summary:
Related to #21485.
Removed `TimerMixin` from `ReactContentSizeUpdateTest`.
Pull Request resolved: https://github.com/facebook/react-native/pull/21502

Reviewed By: TheSavior

Differential Revision: D10218548

Pulled By: RSNara

fbshipit-source-id: 9a0642e14f8548d8dc9683f0f70353416ed04ae0

IntegrationTests/ReactContentSizeUpdateTest.js

@@ -14,7 +14,6 @@ const createReactClass = require('create-react-class');
 const ReactNative = require('react-native');
 const RCTNativeAppEventEmitter = require('RCTNativeAppEventEmitter');
 const Subscribable = require('Subscribable');
-const TimerMixin = require('react-timer-mixin');
 
 const {View} = ReactNative;
 
@@ -27,7 +26,8 @@ const newReactViewHeight = 202;
 
 const ReactContentSizeUpdateTest = createReactClass({
   displayName: 'ReactContentSizeUpdateTest',
-  mixins: [Subscribable.Mixin, TimerMixin],
+  mixins: [Subscribable.Mixin],
+  _timeoutID: (null: ?TimeoutID),
 
   UNSAFE_componentWillMount: function() {
     this.addListenerOn(
@@ -52,11 +52,17 @@ const ReactContentSizeUpdateTest = createReactClass({
   },
 
   componentDidMount: function() {
-    this.setTimeout(() => {
+    this._timeoutID = setTimeout(() => {
       this.updateViewSize();
     }, 1000);
   },
 
+  componentWillUnmount: function() {
+    if (this._timeoutID != null) {
+      clearTimeout(this._timeoutID);
+    }
+  },
+
   rootViewDidChangeIntrinsicSize: function(intrinsicSize) {
     if (
       intrinsicSize.height === newReactViewHeight &&