Remove bad assert

It is possible also in non-SMP case:
1. The process receives an exit signal and is set in status exiting
   and inserted into the run queue.
2. The distribution port exits before the process has been selected
   for execution and cannot remove the link half on the process since
   it is in status exiting.
3. Process is selected for execution and when removing this link half
   the distribution channel is gone!

erts/emulator/beam/erl_process.c

@@ -7980,15 +7980,6 @@ static void doit_exit_link(ErtsLink *lnk, void *vpcontext)
 	    if (rlnk)
 		erts_destroy_link(rlnk);
 	    erts_deref_dist_entry(dep);
-	} else {
-#ifndef ERTS_SMP
-	    /* XXX Is this possible? Shouldn't this link
-	       previously have been removed if the node
-	       had previously been disconnected. */
-	    ASSERT(0);
-#endif
-	    /* This is possible when smp support has been enabled,
-	       and dist port and process exits simultaneously. */
 	}
 	break;