Remove old accessibility enums, finish renaming public interface.

This is the third step in a sequence of patches to refactor
Blink accessibility enums to be able to use them in Chromium.

This step finishes renaming the public interface. Subsequent
changes will continue to rename and refactor Blink
accessibility code to be more consistent as well.

Step 1 (Blink): https://chromiumcodereview.appspot.com/22331005
Step 2 (Chromium): https://codereview.chromium.org/23651003

BUG=269034

Review URL: https://chromiumcodereview.appspot.com/23726007

git-svn-id: svn://svn.chromium.org/blink/trunk@157398 bbb929c8-8fbe-4397-9dbb-9b2b20218538