Course Continue Button is not displayed to non-enrolled students regardless of the enrollment visibility setting.

### Reproduction Steps

1. Create a new course.
2. Add the `Course Continue Button` to the course page.
3. Observe that the `Enrollment Visibility` setting is set to `Everyone`.

### Expected Behavior

The `Enrollment Visibility` setting should not have `Everyone` in the options. Alternatively, it should not have `Enrollment Visibility` at all.

### Actual Behavior

The `Enrollment Visibility` setting has `Everyone` in the options. But, the `Course Continue Button` or the `Get Started` button will not visible on the front-end for non-logged in users, as expected.

Since the `Get Started` is tied to some logic (it relies on looking up what progress the student is on the course so it knows which lesson to link to), we should make sure that the `Enrollment Visibility` setting does not contain `Everyone` as an option since that confuses users.

This issue has be recreated:
+ [x] Locally
+ [ ] On a staging site
+ [x] On a production website
+ [ ] With only LifterLMS and a default theme