parserTests: Do not check for DjVu support

Unnecessary now that we have MockMediaHandlerFactory. Have
MockDjVuHandler::isEnabled() always return true so that we don't have to
hack the configuration. May possibly help the ProofreadPage tests pass
in Jenkins.

Also remove a couple of unnecessary debug log calls.

Change-Id: Ic8aea8fe235b4b5336a7377c4b61379ed06a67ab