Remove unused ui::KeyEvent::unmodified_character_, etc.

Remove unmodified_character_, and its accessors.
Remove related unit test code; re-enable functional tests.
(the tests were fixed by r105549, but never re-enabled?)

BUG=99129,298601
TEST=NONE
R=sadrul@chromium.org

Review URL: https://codereview.chromium.org/25417009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227116 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227116