Remove the last vestige of the internal SDL_IMAGE macros

sc2/src/port.h

@@ -460,18 +460,14 @@ typedef unsigned int wint_t;
 #	endif  /* defined (__FreeBSD__) || defined (__OpenBSD__) */
 #endif  /* defined (PORT_WANT_ERRNO) */
 
-// Use SDL_INCLUDE and SDL_IMAGE_INCLUDE to portably include the SDL files
-// from the right location.
+// Use SDL_INCLUDE to portably include the SDL files from the right location.
 // TODO: Where the SDL and SDL_image headers are located could be detected
 //       from the build script.
 #ifdef __APPLE__
-	// SDL_image.h in a directory SDL_image under the include dir.
 #	define SDL_DIR SDL
-#	define SDL_IMAGE_DIR SDL_image
 #else
 	// SDL_image.h directly under the include dir.
 #	undef SDL_DIR
-#	undef SDL_IMAGE_DIR
 #endif
 
 #ifdef SDL_DIR
@@ -480,12 +476,6 @@ typedef unsigned int wint_t;
 #	define SDL_INCLUDE(file) <file>
 #endif  /* SDL_DIR */
 
-#ifdef SDL_IMAGE_DIR
-#	define SDL_IMAGE_INCLUDE(file) <SDL_IMAGE_DIR/file>
-#else
-#	define SDL_IMAGE_INCLUDE(file) <file>
-#endif  /* SDL_IMAGE_DIR */
-
 // Mark a function as using printf-style function arguments, so that
 // extra consistency checks can be made by the compiler.
 // The first argument to PRINTF_FUNCTION and VPRINTF_FUNCTION is the