Remove obsolete DEBUG and NDEBUG macro dance.

The original intention of this seemed to have been to enable DEBUG when
NDEBUG was not defined within Google3. Everything since then was just
added to avoid the "#error" below checking for consistency from firing.
Semantics have also shifted along the way. I vote for dropping this.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/1315063007

Cr-Commit-Position: refs/heads/master@{#30591}

src/v8.h

@@ -8,22 +8,6 @@
 #include "include/v8.h"
 #include "src/allocation.h"
 
-#if defined(GOOGLE3) || defined(DCHECK_ALWAYS_ON)
-// Google3 and Chromium special flag handling.
-#if defined(DEBUG) && defined(NDEBUG)
-// V8 only uses DEBUG and whenever it is set we are building a debug
-// version of V8. We do not use NDEBUG and simply undef it here for
-// consistency.
-#undef NDEBUG
-#endif
-#endif  // defined(GOOGLE3)
-
-// V8 only uses DEBUG, but included external files
-// may use NDEBUG - make sure they are consistent.
-#if defined(DEBUG) && defined(NDEBUG)
-#error both DEBUG and NDEBUG are set
-#endif
-
 namespace v8 {
 namespace internal {