Don't show GitLab Duo Core banner to Self-Hosted customers

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Description

This Duo Core banner is displayed for Self-Managed users using Duo Self-Hosted:

In the context of Duo Self-Hosted customers, this banner is confusing.

• Duo Core is not available for offline customers, as it relies on the GitLab hosted AI Gateway.
• For online instances, feature settings either use a self-hosted model OR using the vendored model. It cannot be both at the same time– meaning there cannot be users with Duo Seats that are assigned SHM and other users without Duo Seats that use vendored model. There are plans to change this: Enable Self-Hosted Customers to Use GL AI Vendo... (#569772)

We should hide this banner in the context of Duo Self-Hosted customers.

Definition of Done

• Hide the Duo Core banner for Duo Self-Hosted customers.