Revert GCC compilation fix on 3.1 branch that contained an invalid

src/v8globals.h

Index: src/v8globals.h
===================================================================
--- src/v8globals.h	(revision 7609)
+++ src/v8globals.h	(working copy)
@@ -472,11 +472,7 @@
 // The Strict Mode (ECMA-262 5th edition, 4.2.2).
 enum StrictModeFlag {
   kNonStrictMode,
-  kStrictMode,
-  // This value is never used, but is needed to prevent GCC 4.5 from failing
-  // to compile when we assert that a flag is either kNonStrictMode or
-  // kStrictMode.
-  kInvalidStrictFlag
+  kStrictMode
 };
 
 } }  // namespace v8::internal