Remove Sample metrics service, controller and user starred model

What does this MR do and why?

Remove Sample metrics service

Remove sample metrics controller

Remove specs and usages of service and controller

Remove UsersstarredDashboard Model and its pending usage.

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #397139 (closed)