Remove consolidate_mr_analytics_in_shared_dashboards feature flag

What does this MR do and why?

Remove consolidate_mr_analytics_in_shared_dashboards feature flag and related code.

• Adds redirect from the old MR analytics page to the new MR analytics dashboard.
• Remove Analyze > Merge request analytics from the sidebar in all cases
• Removes old controller, HAML view, custom page SCSS and JS entrypoint
• Update references to point to the new page
• Removes the feature flag

Additional frontend code will be removed in a follow-up MR. Some of the code was shared between the old/new apps, so to keep the diff simple I wanted to do it separately

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Navigate to any project
2. Confirm that Analyze > Merge request analytics does not appear in the side menu
3. Test the redirect from old MR analytics page

• Visit the old merge request analytics URL: http://gdk.test:3000/flightjs/flight/-/analytics/merge_request_analytics
• Verify it redirects to http://gdk.test:3000/flightjs/flight/-/analytics/dashboards/merge_request_analytics

4. For any project, navigate to Analyze > Analytics dashboards
5. Open the Merge request analytics dashboard and verify that it loads successfully
6. Open the Value streams dashboard and verify that clicking the Deploys, Merge request throughput and Median time to merge metric names all link to the new dashboard

MR acceptance checklist

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Related to #568363 and #546036 (closed)