Use the Database directly from HttpHandler::GetEntries.

And also CTUDPDNSServer::LeafHash, for completeness.

This momentarily helped prove to myself that I didn't have to consider the thread safety of LogLookup, only that of Database, while I was moving it to the thread pool (in a separate, upcoming pull request). Having one less silly forwarder method is just a bonus. :wink: 

See also: https://codereview.appspot.com/142240043/