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;

include/SDL3/SDL_misc.h

@@ -62,12 +62,12 @@ extern "C" {
  *
  * \param url a valid URL/URI to open. Use `file:///full/path/to/file` for
  *            local files, if supported.
- * \returns SDL_TRUE on success or SDL_FALSE on failure; call SDL_GetError()
+ * \returns true on success or false on failure; call SDL_GetError()
  *          for more information.
  *
  * \since This function is available since SDL 3.0.0.
  */
-extern SDL_DECLSPEC SDL_bool SDLCALL SDL_OpenURL(const char *url);
+extern SDL_DECLSPEC bool SDLCALL SDL_OpenURL(const char *url);
 
 /* Ends C function definitions when using C++ */
 #ifdef __cplusplus