Remove unnecessary div from MarkdownField to apply list styles correctly

What does this MR do?

Remove one level of <div> in the Markdown preview, so the list styles correctly apply.

• https://gitlab.com/gitlab-org/gitlab-ce/blob/b388111f6ed5181c357f5c37277f16c6ae234f5a/app/assets/stylesheets/framework/markdown_area.scss#L134-138
• https://gitlab.com/gitlab-org/gitlab-ce/blob/b388111f6ed5181c357f5c37277f16c6ae234f5a/app/assets/stylesheets/framework/mixins.scss#L106-118

Before	After

What are the relevant issue numbers?

closes https://gitlab.com/gitlab-org/gitlab-ce/issues/55190

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer