Clean up some obsolete NetBSD portability cruft.

Test: treehugger
Change-Id: I9197e6ebcaec6811ff5ee12e4d2e7a14c2881f64
diff --git a/libc/upstream-netbsd/android/include/namespace.h b/libc/upstream-netbsd/android/include/namespace.h
index 630ea9b..ae7585c 100644
--- a/libc/upstream-netbsd/android/include/namespace.h
+++ b/libc/upstream-netbsd/android/include/namespace.h
@@ -14,10 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef _BIONIC_NETBSD_NAMESPACE_H_included
-#define _BIONIC_NETBSD_NAMESPACE_H_included
+#pragma once
 
 __LIBC_HIDDEN__ int __res_enable_mt(void);
 __LIBC_HIDDEN__ int __res_disable_mt(void);
-
-#endif