[zfcampus/zf-apigility#56] Do not return a value!

Returning a value can be used by the object triggering the event to stop 
propagation; as such, any listener that is listening on wildcard events, or, 
typically, more than one event, likely should not return a value.

In this particular case, the logging listener was returning a boolean true 
value. This broke the zf-mvc-auth "authorization" event, as boolean return 
values can be used to short-circuit (they indicate authorization status).

The code inside this method also indicated that the return value was a hack 
until a ZF2 issue was resolved -- and it has been for some time now.

Fixes zfcampus/zf-apigility#56.