Revert 247420 "Add a11y on-screen keyboard."

Suspected of breaking ChromeOS ASan:
http://build.chromium.org/p/chromium.memory.fyi/builders/Chromium%20OS%20%28valgrind%29%285%29/builds/25099/steps/memory%20test%3A%20unit/logs/stdio


> Add a11y on-screen keyboard.
> 
> Adds an accessibility option for displaying a virtual keyboard on the login screen and on the settings page.
> 
> Followup patches required to persist the login preference on first time sign in, and to use the full virtual keyboard in place of the touch optimized version. 
> 
> BUG=297132
> 
> Review URL: https://codereview.chromium.org/137543002

TBR=kevers@chromium.org

Review URL: https://codereview.chromium.org/137023009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247448 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247448