el/wake: remove an invalid assertion

Well it actually seems that we loop sometimes, more investigation is
needed to provide an explanation.

Change-Id: I5083cc3ff433744e115ae2bf0a8b3c3e1858223f
Priv-Id: 97d6a5972691479a96681848fd245253d6798715

Author: skyj

src/core/el.blk

@@ -1660,9 +1660,8 @@ static data_t el_wake_unregister(el_t *elp)
                                              memory_order_acquire) < 0))
         {
             /* Because the eventfd() API already have locks in the kernel we
-             * should actually never loop.
+             * should rarely loop.
              */
-            assert(false);
             cpu_relax();
         }
         el_fd_unregister(&el->wake.event_fd);