proc: update list manipulation comment on process exit

Processes stay in the hash until they get reaped.

This code does not unlink the child from the parent, so remove
the claim that it does.

Sponsored by:	The FreeBSD Foundation

sys/kern/kern_exit.c

@@ -429,8 +429,7 @@ exit1(struct thread *td, int rval, int signo)
 
 	sx_xlock(&proctree_lock);
 	/*
-	 * Remove proc from allproc queue and pidhash chain.
-	 * Place onto zombproc.  Unlink from parent's child list.
+	 * Move proc from allproc queue to zombproc.
 	 */
 	sx_xlock(&allproc_lock);
 	LIST_REMOVE(p, p_list);