Javadoc fix nad remove unused import.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1519704 13f79535-47bb-0310-9956-ffa450edef68
[LOG4J2-374] Add more options to PatternLayout to display more detailed information about a Throwable.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1519707 13f79535-47bb-0310-9956-ffa450edef68