[CI] Remove or replace YAPF disables

[bveeramani]

Several files contain yapf: disable comments.

❯ find . -type f -name "*.py" | xargs grep -l "yapf: disable"
./python/ray/util/sgd/torch/examples/raysgd_torch_signatures.py
./python/ray/util/sgd/torch/examples/tune_example.py
./python/ray/util/sgd/torch/examples/train_example.py
./python/ray/tune/tests/ext_pytorch.py
./python/ray/tune/tests/tutorial.py
./python/ray/tune/result.py
./python/ray/tune/examples/pbt_convnet_example.py
./python/ray/tune/examples/mnist_pytorch_trainable.py
./python/ray/tune/examples/mnist_pytorch_lightning.py
./python/ray/tune/examples/cifar10_pytorch.py
./python/ray/train/examples/torch_quick_start.py
./python/ray/train/examples/tensorflow_quick_start.py
./python/ray/serve/examples/doc/tutorial_tensorflow.py
./python/ray/serve/examples/doc/tutorial_sklearn.py
./python/ray/serve/examples/doc/tutorial_batch.py
./python/ray/serve/examples/doc/tutorial_pytorch.py
./rllib/agents/a3c/a3c.py
./rllib/agents/maml/maml.py
./rllib/agents/sac/sac.py
./rllib/agents/ars/ars.py
./rllib/agents/cql/cql.py
./rllib/agents/ddpg/ddpg.py
./rllib/agents/impala/impala.py
./rllib/agents/mbmpo/mbmpo.py
./rllib/agents/pg/default_config.py
./rllib/agents/dqn/apex.py
./rllib/agents/dqn/simple_q.py
./rllib/agents/dqn/dqn.py
./rllib/agents/dqn/r2d2.py
./rllib/agents/dreamer/dreamer.py
./rllib/agents/trainer.py
./rllib/agents/es/es.py
./rllib/agents/ppo/ddppo.py
./rllib/agents/ppo/appo.py
./rllib/agents/ppo/ppo.py
./rllib/agents/slateq/slateq.py
./rllib/agents/qmix/qmix.py
./rllib/agents/marwil/bc.py
./rllib/agents/marwil/marwil.py
./rllib/utils/exploration/exploration.py
./rllib/models/catalog.py
./rllib/contrib/maddpg/maddpg.py
./rllib/contrib/bandits/agents/lin_ucb.py
./rllib/contrib/bandits/agents/lin_ts.py
./rllib/contrib/random_agent/random_agent.py
./rllib/contrib/alpha_zero/core/alpha_zero_trainer.py
./rllib/env/multi_agent_env.py
./rllib/evaluation/collectors/sample_collector.py
./doc/examples/doc_code/runtime_env_example.py
./doc/examples/doc_code/tf_example.py
./doc/examples/doc_code/torch_example.py

Once we've formatted the Python code with Black (#21316), we should either remove or replace these comments.

If it's still necessary to disable formatting on a chunk of code, then we should replace the yapf: disable with fmt: off. Otherwise, we should remove the annotation altogether.