Close rich text promo in e2e test

What does this MR do and why?

Closes the new rich text promo.

Fixes two stale tests: #418335 (closed) and #418273 (closed)

How to set up and validate locally

From the qa directory:

bundle install
export WEBDRIVER_HEADLESS=false # If you'd like to watch the test in action
export QA_GITLAB_URL="http://gdk.test:3000" # Only needed if GDK is not running on http://127.0.0.1:3000
bundle exec rspec qa/specs/features/browser_ui/2_plan/issue/collapse_comments_in_discussions_spec.rb

MR acceptance checklist

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