Remove unnecessary casts.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1429892 13f79535-47bb-0310-9956-ffa450edef68
Remove unused imports.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1429893 13f79535-47bb-0310-9956-ffa450edef68