Remove SDL_config.h from the public headers

The SDL headers are no longer dependent on the build configuration.

Fixes https://github.com/libsdl-org/SDL/issues/6643 and https://github.com/libsdl-org/SDL/issues/6641

test/testrendercopyex.c

@@ -12,8 +12,6 @@
 /* Simple program:  Move N sprites around on the screen as fast as possible */
 
 #include <stdlib.h>
-#include <stdio.h>
-#include <time.h>
 
 #ifdef __EMSCRIPTEN__
 #include <emscripten/emscripten.h>