Remove `terms_of_service_vue` feature flag

What does this MR do and why?

Related to #343046 (closed)

The terms_of_service_vue feature flag has been enabled for a milestone so it is now time to remove the feature flag.

Screenshots or screen recordings

For context

Before	After
Untitled__2_	Untitled__1_

TOS longer than page	TOS shorter than page

How to set up and validate locally

1. Login as an admin (root user in GDK).
2. Navigate to /admin/application_settings/general.
3. In the Terms of Service and Privacy Policy panel check the All users must accept the Terms of Service and Privacy Policy to access GitLab checkbox and enter some text in the text area. Save the form.
4. Navigate to /admin/users and choose a user.
5. Click Impersonate in the upper right corner.

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.