Fix https://bugzilla.redhat.com/show_bug.cgi?id=927236 remove lock on PageSubscriptionImpl
Reasoning is as follows:
- the method just forwards the call to getPageInfo(boolean, long) which
  is /not/ synchronized on PageSubscriptionImpl but which synchronizes
  on "consumedPages".
- for all I can tell, at PageSubscriptionImpl.getPageInfo(*) we really
  only need to synchronize on consumedPages.