fix the dead-lock bugzilla

https://bugzilla.redhat.com/show_bug.cgi?id=927236
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`.