Duplicated customization notices after Stripe promotional banner was introduced

[wjrosa]

Describe the bug
Since the Stripe promotional banner was merged, the customization notice related to the new checkout experience is displayed twice.

To Reproduce
Steps to reproduce the behavior:

• On a new store, just go to the payments settings screen (/wp-admin/admin.php?page=wc-settings&tab=checkout&section=stripe&panel=settings)
• Notice the duplicated notices

Expected behavior
A single notice should be displayed.

Screenshots