Print Preview: Remove unnecessary extraLibraries

Remove unnecessary extraLibraries from ModelSettingsAvailabilityTest.

These were accidentally left in when Print Preview was migrated to
Polymer 3, and cause the test to throw JS exceptions.

Bug: 1012574
Change-Id: Ifa3a3492231f14acd8d1b6b70fc26334d3dfbb9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1912827Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714760}

chrome/test/data/webui/print_preview/print_preview_ui_browsertest.js

@@ -247,15 +247,6 @@ var PrintPreviewModelSettingsAvailabilityTest = class extends PrintPreviewTest {
   get browsePreload() {
     return 'chrome://print/test_loader.html?module=print_preview/model_settings_availability_test.js';
   }
-
-  /** @override */
-  get extraLibraries() {
-    return super.extraLibraries.concat([
-      '../test_util.js',
-      'print_preview_test_utils.js',
-      'model_settings_availability_test.js',
-    ]);
-  }
 };
 
 TEST_F('PrintPreviewModelSettingsAvailabilityTest', 'All', function() {