Replace CMA-ES with ES in emitter docstrings

[btjanaka]

Description

Since the ES in these emitters is no longer limited to CMA-ES, these docstrings were inaccurate.

TODO

Questions

Status

• [x] I have read the guidelines in CONTRIBUTING.md
• [x] I have formatted my code using yapf
• [x] I have tested my code by running pytest
• [x] I have linted my code with pylint
• [x] ~I have added a one-line description of my change to the changelog in HISTORY.md~
• [x] This PR is ready to go