[w3c/payment-handler] Remove the deprecated basic-card content (#397)

The spec still mentions basic-card although basic-card has been deprecated, e.g., 
* "Some payment methods, such as basic-card expect little to no processing by the payment handler which simply returns payment card details in the response"
* "For example, for the basic-card payment method, this object will consist of an object with two fields: one for supportedNetworks, and another for supportedTypes."
* code example of payment handler registration, registering capabilities

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