Calling destroy() on the UI doesn't remove the spinner or client side ad container elements

[absidue]

Have you read the FAQ and checked for duplicate open issues?
Yes

If the problem is related to FairPlay, have you read the tutorial?
Not applicable

What version of Shaka Player are you using?
4.11.2

Can you reproduce the issue with our latest release version?
Yes

Can you reproduce the issue with the latest code from main?
Yes

Are you using the demo app or your own custom app?
Both

If custom app, can you reproduce the issue using our demo app?
Yes

What browser and OS are you using?
Firefox on Windows 10

For embedded devices (smart TVs, etc.), what model and firmware version are you using?
Not applicable

What are the manifest and license server URIs?
Not applicable

What configuration are you using? What is the output of player.getConfiguration()?
Default

What did you do?
Called destroy() on shaka.ui.Overlay.

What did you expect to happen?
Expected the shaka-spinner-container and shaka-client-side-ad-container elements to be removed from the DOM.

What actually happened?
The shaka-spinner-container and shaka-client-side-ad-container elements still exist in the DOM.

Are you planning send a PR to fix it?
No, because of the CLA, but here is a diff that should fix it:

--- a/ui/controls.js
+++ b/ui/controls.js
@@ -259,6 +259,16 @@ shaka.ui.Controls = class extends shaka.util.FakeEventTarget {
       this.controlsContainer_ = null;
     }
 
+    if (this.spinnerContainer_) {
+      this.videoContainer_.removeChild(this.spinnerContainer_);
+      this.spinnerContainer_ = null;
+    }
+
+    if (this.clientAdContainer_) {
+      this.videoContainer_.removeChild(this.clientAdContainer_);
+      this.clientAdContainer_ = null;
+    }
+
     if (this.castProxy_) {
       await this.castProxy_.destroy();
       this.castProxy_ = null;
@@ -525,6 +535,8 @@ shaka.ui.Controls = class extends shaka.util.FakeEventTarget {
    * @export
    */
   getClientSideAdContainer() {
+    goog.asserts.assert(
+        this.clientAdContainer_, 'No client ad container after destruction!');
     return this.clientAdContainer_;
   }
 
@@ -983,7 +995,7 @@ shaka.ui.Controls = class extends shaka.util.FakeEventTarget {
 
   /** @private */
   addBufferingSpinner_() {
-    /** @private {!HTMLElement} */
+    /** @private {HTMLElement} */
     this.spinnerContainer_ = shaka.util.Dom.createHTMLElement('div');
     this.spinnerContainer_.classList.add('shaka-spinner-container');
     this.videoContainer_.appendChild(this.spinnerContainer_);
@@ -1140,7 +1152,7 @@ shaka.ui.Controls = class extends shaka.util.FakeEventTarget {
    * @private
    */
   addClientAdContainer_() {
-    /** @private {!HTMLElement} */
+    /** @private {HTMLElement} */
     this.clientAdContainer_ = shaka.util.Dom.createHTMLElement('div');
     this.clientAdContainer_.classList.add('shaka-client-side-ad-container');
     shaka.ui.Utils.setDisplay(this.clientAdContainer_, false);