Tracing: Remove UI at Monitor > Tracing and left nav item

Problem to solve

In 15.0, we disabled the Tracing features via a feature flag. As part of this work, we'll need to delete code for the Tracing landing page and left-navigation item.

⚠ Removal should take place in %15.2 or later.

Tracking issue for deprecation & removal: Monitor: Tracing Deprecation (#346540 - closed)

Proposal

Remove tracing landing page. Remove tracing from the left-navigation.

This has both backend and frontend pieces. It would be most convenient to be done by a single engineer, full stack.

Intended users

Metrics

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