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/testutils.c

@@ -149,3 +149,5 @@ LoadTexture(SDL_Renderer *renderer, const char *file, SDL_bool transparent,
     }
     return texture;
 }
+
+/* vi: set ts=4 sw=4 expandtab: */