Removes commented-out section from capybara page

What does this MR do?

Removes language from doc/development/testing_guide/end_to_end/capybara_to_chemlab_migration_guide.md identified in #413204 (closed). This information has been commented out since at least February 2021, since Integrate Chemlab into QA test suite (!54589 - merged).

Documentation is supposed to represent the current state of the product; this information shouldn't be included -- even commented-out -- at this time. We should either uncomment it or remove it. @ddavison, as you were the person who introduced it, I'm adding you as a reviewer. Hopefully you'll know whether to uncomment or remove.

Related issues

Related to HTML comments in documentation markdown files (#413204 - closed)

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