Removed un-used imports in HostDb

git-svn-id: https://svn.apache.org/repos/asf/nutch/trunk@1560436 13f79535-47bb-0310-9956-ffa450edef68
NUTCH-1413 Record response time

git-svn-id: https://svn.apache.org/repos/asf/nutch/trunk@1560512 13f79535-47bb-0310-9956-ffa450edef68