runtime: remove no longer used enums for openbsd

The code that used these has been moved to lock_sema.c.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5376062

src/pkg/runtime/openbsd/thread.c

@@ -8,14 +8,6 @@
 
 enum
 {
-	MUTEX_UNLOCKED = 0,
-	MUTEX_LOCKED = 1,
-	MUTEX_SLEEPING = 2,
-
-	ACTIVE_SPIN = 4,
-	ACTIVE_SPIN_CNT = 30,
-	PASSIVE_SPIN = 1,
-
 	ESRCH = 3,
 	ENOTSUP = 91,