chore: clean up dev environment from set-testing workflow

Description

This pull request resolves #188186752.

Updates the config.yml file by cleaning up the duplicated environment variables that were set in the set-accessibility-testing-env-vars section and set-content-env-vars
Adds a comment in both the set-accessibility-testing-env-vars and set-content-env-vars
Note that the step set-dev-env-vars is referenced in both the deploy-content and deploy-accessibility-testing workflows on line 629 and 645

[X] I have rebased this branch from the latest main branch
[X] I have performed a self-review of my code
[X] I have created and/or updated relevant documentation on the engineering documentation website
[X] I have not used any relative imports
[X] I have pruned any instances of unused code
[X] I have not added any markdown to labels, titles and button text in config
[X] If I added/updated any values in userData (including profileData, formationData etc), then I added a new migration file
[X] I have checked for and removed instances of unused config from CMS
[X] If I added any new collections to the CMS config, then I updated the search tool and cmsCollections.ts (see CMS Additions in Engineering Reference/FAQ on the engineering documentation site)
[X] I have updated relevant .env values in both .env-template and in Bitwarden