chore: fix doc bug for AI Settings

This change updates the documentation for turning off GitLab Duo in version 17.7. It clarifies that the instructions apply to turning off GitLab Duo for a group, including its subgroups and projects. The note has been revised to specify that in GitLab 17.7, users cannot turn off GitLab Duo for groups or subgroups in GitLab Self-Managed, whereas previously it only mentioned subgroups. The update also removes a reference to GitLab Self-Managed from the main instruction, making it more general. The prerequisites section is now empty, suggesting that any previous requirements have been removed or are yet to be added.