What files are needed for the AWS EB CLI 3.x tools?

I've recently switched from old AWS EB CLI tools (2.6.4) to the current ones (3.0.10) and am wondering how to ensure that my project's configuration is migrated, and what configuration files I should keep.

I've run (the new version of) eb init and now have, in my project's .elasticbeanstalk directory, a new file

config.yml

along with several ones that were there before

config
optionsettings.sitetest-develop-env
optionsettings.sitetest-env

which of these are still needed; which can I delete; and what steps to I need to take to ensure that all of the old settings have been migrated to (and to the right place for) the 3.x AWS EB CLI tools?