EventManager: Rename queue accessor and remove cast operator

EventManager: Rename queue accessor and remove cast operator

This patch renames the queue() accessor to the less ambigious
eventQueue, and also removes the cast operator. The queue() member
function cause problems in derived classes that declare members with
the same name, e.g. a MemObject subclass that has a packet queue on
its own. The operator is not causing any harm at this point, but as it
is not used there is little point in keeping it.