Re-enable CrExtensionsItemListTest.NoItems which was flaky on Mac 10.9

Mac 10.9 is no longer supported, so try re-enabling this test, since
it was disabled for flakes that only happened on this platform.

Meant to do this in
https://chromium-review.googlesource.com/c/chromium/src/+/1833794
but missed this test.

Bug: 771099
Change-Id: I074beeef149b058eaa1b374ecdcc6a1c936d6307
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1850967
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704670}

chrome/test/data/webui/extensions/cr_extensions_browsertest.js

@@ -398,13 +398,7 @@ TEST_F('CrExtensionsItemListTest', 'Filtering', function() {
   this.runMochaTest(extension_item_list_tests.TestNames.Filtering);
 });
 
-// This test is flaky on Mac10.9 Tests (dbg). See https://crbug.com/771099.
-GEN('#if defined(OS_MACOSX)');
-GEN('#define MAYBE_NoItems DISABLED_NoItems');
-GEN('#else');
-GEN('#define MAYBE_NoItems NoItems');
-GEN('#endif');
-TEST_F('CrExtensionsItemListTest', 'MAYBE_NoItems', function() {
+TEST_F('CrExtensionsItemListTest', 'NoItems', function() {
   this.runMochaTest(extension_item_list_tests.TestNames.NoItemsMsg);
 });