netbsd-compat.h: remove a couple more unused #defines.

We no longer compile any code that needs these.

Change-Id: Ia22d6f33e24a361f80d8ceda7638050c7d9c83d4
diff --git a/libc/upstream-netbsd/android/include/netbsd-compat.h b/libc/upstream-netbsd/android/include/netbsd-compat.h
index 854b19f..dc52002 100644
--- a/libc/upstream-netbsd/android/include/netbsd-compat.h
+++ b/libc/upstream-netbsd/android/include/netbsd-compat.h
@@ -35,8 +35,4 @@
  */
 #define __UNCONST(a)    ((void *)(unsigned long)(const void *)(a))
 
-// TODO: we don't yet have thread-safe environment variables.
-#define __readlockenv() 0
-#define __unlockenv() 0
-
 #define __arraycount(a) (sizeof(a) / sizeof(a[0]))