Is it possible to turn off (or hide) the ability to generate or access Acceptance Tests?
No, you are not able to turn off Acceptance Tests. Acceptance Tests represent acceptance criteria and are typically created during the Product Planning phase, and then further refined during Sprint/Iteration Planning. Acceptance tests are called "tests" and define the required behavior of a completed item. Tests can be added to any of the following items: stories, defects, portfolio items, test sets, story templates, and defect templates.
If you would like for us to consider adding the ability to turn off this feature, please add this as a new feature request out on IdeaSpace. We will consider it as an enhancement to the Lifecycle product.