Remove "Introducing standalone vulnerabilities" banner from Security Dashboards

Problem to solve

As part of introducing Standalone Vulnerabilities on our Security Dashboards (#13561 (closed)) we alerted our customers to this change by introducing a banner to the top of the Project level dashboard (#210358 (closed)).

This banner is not permanent and we need to remove it when we believe we've sufficiently informed customers of this change.

Proposal

Remove the banner

Other links/references

Technical Details

Essentially revert this commit, which added the banner

• frontend remove banner from UI
• frontend remove tests regarding the banner