Replace accessibility-developer-tools submodule with accessibility-audit directory containing just the generated axs_testing.js file

Follow-up CL will remove accessibility-developer-tools from DEPS.

BUG=165901

Review URL: https://chromiumcodereview.appspot.com/23830003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224794 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 224794