add comment for #4407 and remove seemingly unnecessary cudnn.enabled

def enable_tf32():

    if torch.cuda.is_available():

        # enabling benchmark option seems to enable a range of cards to do fp16 when they otherwise can't

        # see https://github.com/AUTOMATIC1111/stable-diffusion-webui/pull/4407

        if any([torch.cuda.get_device_capability(devid) == (7, 5) for devid in range(0, torch.cuda.device_count())]):

            torch.backends.cudnn.benchmark = True

            torch.backends.cudnn.enabled = True

        torch.backends.cuda.matmul.allow_tf32 = True

        torch.backends.cudnn.allow_tf32 = True