[filesapp] SWA volumeManager fake defines addEventListener() twice

Remove definition of addEventListener() and retain the definition that
takes arguments addEventListener(type, name).

Bug: 1113981
Change-Id: Ibf97bf6a7cef740a58ad96e2823c39150f2b7554
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2606405
Auto-Submit: Noel Gordon <noel@chromium.org>
Commit-Queue: Alex Danilo <adanilo@chromium.org>
Reviewed-by: Alex Danilo <adanilo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#839671}

chromeos/components/file_manager/resources/file_manager_fakes.js

@@ -230,8 +230,6 @@ window.VolumeManager = class {
     this.volumeInfoList = new VolumeInfoListFake();
   }
 
-  addEventListener() {}
-
   /**
    * Disposes the instance. After the invocation of this method, any other
    * method should not be called.