[SYCL] Remove branch which is never taken

Event is retained explicitely when created to ensure that the event is
not destroyed before it is really signalled. It is release in
Event->cleanup after event is singalled. This means that if reference
count for an event is zero then cleanup was already called for this
event and is not going to be called anymore.

Author: againull

sycl/plugins/level_zero/pi_level_zero.cpp

@@ -5224,9 +5224,6 @@ static pi_result EventRelease(pi_event Event, pi_queue LockedQueue) {
   }
 
   if (--(Event->RefCount) == 0) {
-    if (!Event->CleanedUp)
-      Event->cleanup(LockedQueue);
-
     if (Event->CommandType == PI_COMMAND_TYPE_MEM_BUFFER_UNMAP &&
         Event->CommandData) {
       // Free the memory allocated in the piEnqueueMemBufferMap.