Docs: clarify prerequisites for project deletion

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/490915

Cover an edge case that prevents users from deleting a project.

doc/administration/settings/visibility_and_access_controls.md

@@ -65,6 +65,11 @@ To restrict project deletion to only administrators:
    - (GitLab 15.0 and earlier) **Default project deletion protection**, and select **Only admins can delete project**.
 1. Select **Save changes**.
 
+To disable the restriction:
+
+1. Select **Owners and administators**.
+1. Select **Save changes**.
+
 ## Deletion protection
 
 DETAILS:

doc/user/project/working_with_projects.md

@@ -156,6 +156,7 @@ After you delete a project:
 Prerequisites:
 
 - You must have the Owner role for a project.
+- Owners must be [allowed to delete projects](../../administration/settings/visibility_and_access_controls.md#restrict-project-deletion-to-administrators).
 
 To delete a project: