Remove duplicate load state notification to ChromeVox.

BUG=261451
TEST=On Chrome OS, rapidly enable/disable spoken feedback on user/lock/oobe screens.
TBR=dmazzoni@chromium.org

Review URL: https://codereview.chromium.org/60373002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233180 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233180