Remove old product analytics features

What does this MR do and why?

• "Product Analytics" used to be owned by devopsmonitor but has not been developed since 13.3.
  • The removed functionality is behind a default-off feature flag and has been ever since it was commited to the codebase.
• sectionanalytics groupproduct analytics is building an internal preview of new features for product analytics.
• This MR refactors or removes all of the code, feature flags and associated documentation for these old features so that they no longer cause confusion and removes the risk of namespace collisions.

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 #375499 (closed)