Revert "Re-enable ChromeVoxBackground*.NavigationSyncSelect"

This reverts commit f0f922f7.

Reason for revert: Failing flakily on Linux Chromium OS ASan LSan Tests (1):
- https://ci.chromium.org/p/chromium/builders/ci/Linux%20Chromium%20OS%20ASan%20LSan%20Tests%20%281%29/37738
- https://ci.chromium.org/p/chromium/builders/ci/Linux%20Chromium%20OS%20ASan%20LSan%20Tests%20%281%29/37731
- https://ci.chromium.org/p/chromium/builders/ci/Linux%20Chromium%20OS%20ASan%20LSan%20Tests%20%281%29/37729

Original change's description:
> Re-enable ChromeVoxBackground*.NavigationSyncSelect
>
> Mostly speculative; pass with
>
> testing/xvfb.py out/d/browser_tests --gtest_filter=ChromeVox*.NavigationSyncsSelect
> !! & !! & !! & !! &
>
> TBR=dtseng@chromium.org
>
> Fixed: 976105
> Change-Id: Ieb646dd0ab22d4b45f2355c89542a59c51af5888
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2209684
> Reviewed-by: David Tseng <dtseng@chromium.org>
> Commit-Queue: David Tseng <dtseng@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#770789}

TBR=dtseng@chromium.org

Change-Id: I32c4f0d36e7334cd99e51a25b960d9b56fa32d17
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2213524Reviewed-by: Marina Ciocea <marinaciocea@chromium.org>
Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771563}

chrome/browser/resources/chromeos/accessibility/chromevox/background/background_test.js

@@ -1582,7 +1582,7 @@ TEST_F('ChromeVoxBackgroundTest', 'NavigationEscapesEdit', function() {
       });
 });
 
-TEST_F('ChromeVoxBackgroundTest', 'NavigationSyncsSelect', function() {
+TEST_F('ChromeVoxBackgroundTest', 'DISABLED_NavigationSyncsSelect', function() {
   const mockFeedback = this.createMockFeedback();
   this.runWithLoadedTree(
       `