Remove deprecated OJ_USE_SSE4_2 define

Use only compiler-provided __SSE4_2__ define for SIMD detection.
The old OJ_USE_SSE4_2 macro is no longer needed since we rely on
compiler flags (-msse4.2) which automatically define __SSE4_2__.

This simplifies the code and removes legacy configuration.

Author: sebyx07

ext/oj/simd.h

@@ -9,7 +9,8 @@
 #define HAVE_SIMD_X86 1
 
     // SSE4.2 support (Intel Core i7+, AMD Bulldozer+)
-    #if defined(__SSE4_2__) || defined(OJ_USE_SSE4_2)
+    // Enabled automatically when compiler has -msse4.2 flag
+    #if defined(__SSE4_2__)
     #define HAVE_SIMD_SSE4_2 1
     #include <nmmintrin.h>
     #endif