Remove issue w3c#48 label.

Fixes w3c#48.

PR w3c#162 refactored the supportedMethods and payment specific data
fields. Issue w3c#3 discusses supporting multiple currencies and issue w3c#4
discusses price per payment method and we should consider specific
proposals for those issues.

PR w3c#162 replaces the `sequence<DOMString>` with
`sequence<PaymentMethodData>` so we now use objects.

specs/paymentrequest.html

@@ -354,12 +354,6 @@ <h2>PaymentRequest constructor</h2>
           for a deposit, pre-auth for a later payment, making recurring payments, and more.
         </div>
 
-        <div class="issue" data-number="48" title="Should list of accepted payment methods be strings or objects?">
-          There is an open issue about whether the list of supported payment
-          methods should be passed to the user agent as a simple sequence of
-          strings or as a more complex and flexible object structure.
-        </div>
-
         <div class="issue" data-number="51" title="Should the payment API be more conversational or less conversational?">
           There is an open issue regarding whether the current pattern of using
           events for exchange of data between the user agent and the website is