Remove description about `optuna study optimize` from examples and docs.

Motivation

#1384 deprecated the optuna study optimize command, but many examples have descriptions about it at the top of the files. I think we can remove them for consistency.

Description

Please remove the descriptions about optuna study optimize from example files.

• docs/source/faq.rst (this section)
• docs/source/tutorial/cli.rst
• docs/source/tutorial/configurations.rst
• examples/allennlp/allennlp_jsonnet.py
• examples/allennlp/allennlp_simple.py
• examples/catalyst_simple.py
• examples/catboost_simple.py
• examples/chainer_simple.py
• examples/dask_ml_simple.py
• examples/keras_simple.py
• examples/lightgbm_simple.py
• examples/lightgbm_tuner_cv.py
• examples/lightgbm_tuner_simple.py
• examples/mxnet_simple.py
• examples/optuna_search_cv_simple.py
• examples/pytorch_ignite_simple.py
• examples/pytorch_lightning_simple.py
• examples/pytorch_simple.py
• examples/quadratic_simple.py
• examples/skimage_lbp_simple.py
• examples/sklearn_additional_args.py
• examples/sklearn_simple.py
• examples/tensorflow_eager_simple.py
• examples/tensorflow_estimator_simple.py
• examples/xgboost_simple.py

Example

This is just an example of the fix. Please feel free to change it depending on the examples.

Before:

We have the following two ways to execute this example:

(1) Execute this code directly.
    $ python quadratic_simple.py


(2) Execute through CLI.
    $ STUDY_NAME=`optuna create-study --storage sqlite:///example.db`
    $ optuna study optimize quadratic_simple.py objective --n-trials=100 --study-name $STUDY_NAME \
      --storage sqlite:///example.db

After:

You can run this example as follows:
    $ python quadratic_simple.py

[ritvik1512]

I have added PR #1566 that should address the removal of optuna study optimize from examples.

[ritvik1512]

Thank you for taking the time to list out the steps, I’ll start with #1 for now.