Remove CreditCard comparisons, objects passed in are not necessarily ActiveMerchant::Billing::CreditCards

@ntalbott @jduff 
This fixes the CreditCard and Check comparisons introduced to Payflow in e38d083b4562844bfe8b1e8843426ab0b516325e

We can't do this because the objects passed in are not necessarily ActiveMerchant::Billing::CreditCards