Add DeleteQueue method to Inspector

- Added ErrQueueNotFound and ErrQueueNotEmpty type to indicate the kind
  of an error returned from the method.

internal/rdb/inspect.go

@@ -745,7 +745,6 @@ func (r *RDB) RemoveQueue(qname string, force bool) error {
 			return err
 		}
 	}
-
 	return r.client.SRem(base.AllQueues, qname).Err()
 }