Remove review_apps page from global navigation

What does this MR do and why?

Describe why, not just what. Include links to relevant issues or discussions.

This mr removes doc page from global navigation. It is related to deprecated functionality removal from gitlab-org/gitlab project. Remove 'gitlab' review-app pipeline code (gitlab-org/gitlab!210475 - merged)

Related to: Remove review-apps documentation from gitlab-or... (gitlab-org/gitlab#578665 - closed)

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