test: Remove global Util alias

There was an alias to shaka.test.Util in a global context which was
affecting other tests.  The result was that these tests could refer to
"Util" without the namespace or their own alias, and everything would
work.

The problem with that is that when the file with the global alias was
removed or disabled, those other tests would fail because "Util" would
be undefined.

This removes the global alias and adds missing local aliases to the
test suites that were accidentally relying on the global one.

Change-Id: Ifca8c1ada0c3e46cb30a2039b5c4c2252d992d37

test/cea/mp4_cea_parser_unit.js

@@ -11,6 +11,7 @@ goog.require('shaka.util.Error');
 describe('Mp4CeaParser', () => {
   const ceaInitSegmentUri = '/base/test/test/assets/cea-init.mp4';
   const ceaSegmentUri = '/base/test/test/assets/cea-segment.mp4';
+  const Util = shaka.test.Util;
 
   /** @type {!ArrayBuffer} */
   let ceaInitSegment;

test/player_integration.js

@@ -36,6 +36,8 @@ describe('Player', () => {
   /** @type {shaka.test.Waiter} */
   let waiter;
 
+  const Util = shaka.test.Util;
+
   beforeAll(async () => {
     video = shaka.test.UiUtils.createVideoElement();
     document.body.appendChild(video);

test/ui/text_displayer_layout_unit.js

@@ -15,11 +15,11 @@ goog.require('shaka.text.UITextDisplayer');
 goog.require('shaka.ui.Overlay');
 goog.require('shaka.util.EventManager');
 
-const Util = shaka.test.Util;
-
 // TODO: Move this suite to the text/ folder where it belongs
-filterDescribe('TextDisplayer layout', Util.supportsScreenshots, () => {
+const supportsScreenshots = () => shaka.test.Util.supportsScreenshots();
+filterDescribe('TextDisplayer layout', supportsScreenshots, () => {
   const UiUtils = shaka.test.UiUtils;
+  const Util = shaka.test.Util;
 
   /** @type {!shaka.extern.TextDisplayer} */
   let textDisplayer;