[VSA] Remove total time chart stage dropdown

What does this MR do and why?

Removes the VSA total time (duration chart) stage dropdown

• Updates related specs
• Updates the total time (duration chart) calculations

This MR also fixes #349555 (closed), as we are removing the dropdown all togethor.

Screenshots or screen recordings

Before	After

How to set up and validate locally

Group VSA seeding instructions

1. Ensure you have an EE license, or stub the cycle_analytics_for_groups license feature to true

2. Create a group

3. Create a project within a group (make sure to initialize the project with a readme, or create it from a template)

4. Seed some test VSA data

   $ VSA_SEED_PROJECT_ID=<project-id> VSA_ISSUE_COUNT=10 SEED_VSA=true FILTER=cycle_analytics rake db:seed_fu

Viewing the chart

1. Navigate to value stream analytics for the group, ie for a project named clean-vsa-project in group new-vsa-group it would be http://<gdk>/groups/:group_id/-/analytics/value_stream_analytics (or find it in the left menu)

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 #322126 (closed)