Allow maintainers to remove pages

What does this MR do?

Shows maintainers "Remove pages button", which is already permitted for them to do.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/54726

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Security reports checked/validated by reviewer