Bug 573137: Revert a change to zutil.h in changeset fb3a132de4ec.

The availability of vsnprintf in recent versions of MSVC has been
addressed in zlib 1.2.3.5 (8 Jan 2010).  r=n/a a=blocking2.0:final

modules/zlib/src/zutil.h

@@ -177,8 +177,7 @@ extern const char * const z_errmsg[10]; /* indexed by 2-zlib_error */
 
          /* functions */
 
-#if defined(STDC99) || (defined(__TURBOC__) && __TURBOC__ >= 0x550) || \
-   (defined(_MSC_VER) && _MSC_VER >= 1500)
+#if defined(STDC99) || (defined(__TURBOC__) && __TURBOC__ >= 0x550)
 #  ifndef HAVE_VSNPRINTF
 #    define HAVE_VSNPRINTF
 #  endif