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/testfilesystem.c

@@ -11,7 +11,6 @@
 */
 /* Simple test of filesystem functions. */
 
-#include <stdio.h>
 #include "SDL.h"
 
 int
@@ -58,3 +57,5 @@ main(int argc, char *argv[])
     SDL_Quit();
     return 0;
 }
+
+/* vi: set ts=4 sw=4 expandtab: */