Moved the SDL version back to SDL_version.h

Added a comment at the top of SDL.h with the current version, for informational purposes

include/SDL3/SDL.h

@@ -22,20 +22,12 @@
 /**
  *  \file SDL.h
  *
- *  Main include header for the SDL library
+ *  Main include header for the SDL library, version 3.1.2
  */
 
 #ifndef SDL_h_
 #define SDL_h_
 
-/**
- * The current version of SDL
- */
-#define SDL_MAJOR_VERSION   3
-#define SDL_MINOR_VERSION   1
-#define SDL_MICRO_VERSION   2
-
-
 #include <SDL3/SDL_stdinc.h>
 #include <SDL3/SDL_assert.h>
 #include <SDL3/SDL_atomic.h>