src: deduplicate CHECK_EQ/CHECK_NE macros

DRY the macros, there is no need to define them twice depending on
whether NDEBUG is defined or not.

src/util.h

@@ -49,15 +49,14 @@ namespace node {
   do {                                                                        \
     if (!(expression)) abort();                                               \
   } while (0)
-# define CHECK_EQ(a, b) CHECK((a) == (b))
-# define CHECK_NE(a, b) CHECK((a) != (b))
 #else
 # define ASSERT(expression)  assert(expression)
 # define CHECK(expression)   assert(expression)
-# define CHECK_EQ(a, b)      assert((a) == (b))
-# define CHECK_NE(a, b)      assert((a) != (b))
 #endif
 
+#define CHECK_EQ(a, b) CHECK((a) == (b))
+#define CHECK_NE(a, b) CHECK((a) != (b))
+
 #define UNREACHABLE() abort()
 
 // If persistent.IsWeak() == false, then do not call persistent.Reset()