Merged from kern_thread.c 1.113, avoid a panic in cpu_throw when the first

thread of a multithreaded process exits.

This unrelated and possibly wrong change was not mentioned in the commit
message for kern_thread.c 1.113.

sys/kern/kern_thr.c

@@ -101,7 +101,9 @@ thr_exit1(void)
 	PROC_UNLOCK(p);
 	td->td_kse = NULL;
 	td->td_state = TDS_INACTIVE;
+#if 0
 	td->td_proc = NULL;
+#endif
 	td->td_ksegrp = NULL;
 	td->td_last_kse = NULL;
 	thread_stash(td);