Remove legacy vsd app

What does this MR do and why?

Cleans up the legacy VSD code. With Migrate Value streams dashboard to shared analy... (!151845 - merged) we removed the group_analytics_dashboard_dynamic_vsd feature flag and all code to toggle between the feature flag states.

This MR removes the legacy code that is no longer used, this was used to render the built in value streams dashboard, but we have now moveed entirely to the shared analytics dashboard framework.

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Screenshots or screen recordings

No visual changes

How to set up and validate locally

All tests passing

Related to #441206 (closed)