Removed SDL_bool in favor of plain bool

We require stdbool.h in the build environment, so we might as well use the plain bool type.

If your environment doesn't have stdbool.h, this simple replacement will suffice:
typedef signed char bool;

test/testutils.h

@@ -16,7 +16,7 @@
 
 #include <SDL3/SDL.h>
 
-SDL_Texture *LoadTexture(SDL_Renderer *renderer, const char *file, SDL_bool transparent,
+SDL_Texture *LoadTexture(SDL_Renderer *renderer, const char *file, bool transparent,
                          int *width_out, int *height_out);
 char *GetNearbyFilename(const char *file);
 char *GetResourceFilename(const char *user_specified, const char *def);