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/testautomation_pixels.c

@@ -1,9 +1,6 @@
 /**
  * Pixels test suite
  */
-
-#include <stdio.h>
-
 #include "SDL.h"
 #include "SDL_test.h"
 
@@ -424,3 +421,5 @@ SDLTest_TestSuiteReference pixelsTestSuite = {
     pixelsTests,
     NULL
 };
+
+/* vi: set ts=4 sw=4 expandtab: */