Update pre-enforcement banner text amendment

What does this MR do and why?

It removes a link and updates the text of the pre-enforcement banner as described in #368870+.

Note: the related feature flag isn't enabled on production.

Screenshots or screen recordings

location	before	after
group
user preferences

How to set up and validate locally

• From rails console enable the feature flag Feature.enable(:namespace_storage_limit_show_preenforcement_banner)
• Visit a group in local GitLab instance
• Visit current user preferences page

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.