Removed environments.scss file and its config

What does this MR do and why?

Removed environments.scss file as ee/app/assets/stylesheets/page_bundles/environments.scss file is not used anymore, removed the file and its config.

Resolves the issue #367793 (closed)

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #367793 (closed)