ExceptionState has some code that was useful during the
transition from ExceptionCode. Remove that code now that
the code base has switched to ExceptionState.

This removes the to bool, to ExceptionCode as well as assign from
ExceptionCode

BUG=252233

Review URL: https://chromiumcodereview.appspot.com/22274002

git-svn-id: svn://svn.chromium.org/blink/trunk@155556 bbb929c8-8fbe-4397-9dbb-9b2b20218538