Remove progress bar during subscriptions

What does this MR do and why?

• Removes the progress bar from last step in subscription registrations
  • at some point in time the progress bar was removed from all steps on subscription registration except the group creation step. We'll fix that here. See further discussion in #414736 (closed)
• Moves WelcomeHelper to proper code path as there is no foss counterpart.
• Resolve some rubocop exceptions on files touched.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Setup to simulate SaaS and restart GDK
2. Visit a group's subscription page like /-/subscriptions/groups/flightjs/edit

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 #414736 (closed)