Remove total_visitors metric from dashboard breakdown reports

[macobo]

Changes

This metric was only shown in some details modals and ~~with scroll depth goals incoming~~ IMO cause confusion and complexity.

Long-term we plan to show the fraction(s) in tooltips.

Follow-up to https://github.com/plausible/analytics/pull/4999

Tests

• [x] Automated tests have been added
• [ ] This PR does not require tests

Changelog

• [x] Entry has been added to changelog
• [ ] This PR does not make a user-facing change

Documentation

• [ ] Docs have been updated
• [ ] This change does not need a documentation update

Dark mode

• [ ] The UI has been tested both in dark and light mode
• [ ] This PR does not change the UI

[github-actions[bot]]

Preview environment👷🏼‍♀️🏗️
PR-5058