Delete CODE_OF_CONDUCT.md (#3452)

The CoC has been added to the .github repo as a community health file (CHF) – which means it will now appear in all of Parsl's repos without needing to create separate CoC files in each. I've tested it and it is appearing in all of our public repos that do not have their own CoC file.

CHF files help automate and standardize various aspects of our project's development and community interaction. They are essential for promoting transparency, good practices, and collaboration in open source projects. More info: https://docs.github.com/en/communities/setting-up-your-project-for-healthy-contributions/creating-a-default-community-health-file#supported-file-types

Co-authored-by: Ben Clifford <benc@hawaga.org.uk>