Removing @Override from interface implementations to maintain Java 1.5 compatibility.

Review at http://gwt-code-reviews.appspot.com/1346801

Review by: scottb@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9685 8db76d5a-ed1c-0410-87a9-c151d255dfc7