Update path to Usage Statistics in Admin Settings

What does this MR do?

Corrects the path to the Usage Statistics section of the Admin Settings page.

Note, I think that https://gitlab.com/gitlab-org/gitlab-ce/commit/3bb720ef65e9678b96decd6815838054189f6f68 is the change that moved the location of the Usage Statistics page from where the docs currently say it is.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content