8034912: backport of 8031737 to jdk8u breaks linux buld.

Reviewed-by: mchung

src/share/native/java/net/net_util.h

@@ -42,9 +42,6 @@
 #define NET_ERROR(env, ex, msg) \
 { if (!(*env)->ExceptionOccurred(env)) JNU_ThrowByName(env, ex, msg) }
 
-#define CHECK_NULL(x) if ((x) == NULL) return;
-#define CHECK_NULL_RETURN(x, y) if ((x) == NULL) return y;
-
 /************************************************************************
  * Cached field IDs
  *