Fix broken links to removed performance-indicators page

Summary

The /handbook/engineering/development/performance-indicators/ page no longer exists, but there are still links to it in the workflow documentation.

This MR removes the broken links and updates the text to note that OMRT and OMA metrics are tracked in internal Tableau dashboards.

Details

Found while working on !19609 - the hugolint job caught broken links in new content, which led to discovering these same broken links exist in the baseline.