Fix path to STS null selection earcon.

Bug: 1166803
Change-Id: I960aab4e3af48fc48b377db1493eba4bc98fe241
AX-Relnotes: n/a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2630427
Auto-Submit: Katie Dektar <katie@chromium.org>
Commit-Queue: Katie Dektar <katie@chromium.org>
Commit-Queue: Akihiro Ota <akihiroota@chromium.org>
Reviewed-by: Akihiro Ota <akihiroota@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843791}

chrome/browser/resources/chromeos/accessibility/select_to_speak/select_to_speak.js

@@ -225,8 +225,7 @@ export class SelectToSpeak {
     this.intervalId_;
 
     /** @private {Audio} */
-    this.null_selection_tone_ =
-        new Audio('select_to_speak/earcons/null_selection.ogg');
+    this.null_selection_tone_ = new Audio('earcons/null_selection.ogg');
 
     /** @private {PrefsManager} */
     this.prefsManager_ = new PrefsManager();