Revert "[Spec] Only allow SPC authentication if in a foreground tab (#…

…238)"

This reverts commits 4a9d883 and
fd37ebe

This behavior is now spec'd in Payment Request itself as of
w3c/payment-request@cce8f5e,
and so does not need to additionally be spec'd in SPC.

spec.bs

@@ -702,22 +702,11 @@ input {{SecurePaymentConfirmationRequest}} |data|, are:
 
 <wpt>
   constructor.https.html
-  authentication-disallowed-when-hidden.https.html
   authentication-invalid-icon.https.html
   authentication-icon-data-url.https.html
   authentication-rejected.https.html
 </wpt>
 
-1. If [=this's=] [=relevant global object=]'s [=associated Document=]'s
-    [=Document/visibility state=] is not `"visible"`, return `false`.
-
-    Note: This prevents SPC from being triggered from a background tab,
-    minimized window, or other similar hidden situations.
-
-    Issue: [=this=] is the {{PaymentRequest}} whose {{PaymentRequest/show()}}
-    method invoked these [=steps to check if a payment can be made=]. It
-    would be better to run this step directly from {{PaymentRequest/show()}}.
-
 1. If |data|["{{SecurePaymentConfirmationRequest/payeeOrigin}}"] is present:
 
     1. Let |parsedURL| be the result of running the [=URL parser=] on