Follow-up from refactor insertCode Button from CSS based solution to dependency injection

The following discussion from gitlab-org/gitlab-ui!4357 (merged) should be addressed:

• @jannik_lehmann started a discussion: (+1 comment)

  Question: Just hiding the custom element isn't the most elegant way to solve this, we could just leverage the expected dependency injection to render the button dynamically?

  Answer: Yes, we could, and we should. However, the current state is a working first iteration, and the MR is already quite large. For the sake of efficiency, I’d like to revisit this in a follow-up and use the CSS approach for now.