Remove a duplicate definition that is already in SDL_guid.h

include/SDL3/SDL_joystick.h

@@ -821,8 +821,6 @@ extern SDL_DECLSPEC const char * SDLCALL SDL_GetJoystickSerial(SDL_Joystick *joy
  */
 extern SDL_DECLSPEC SDL_JoystickType SDLCALL SDL_GetJoystickType(SDL_Joystick *joystick);
 
-extern SDL_DECLSPEC SDL_GUID SDLCALL SDL_GUIDFromString(const char *pchGUID);
-
 /**
  * Get the device information encoded in a SDL_GUID structure.
  *