[in-commerce] Drop support for "Google Checkout" [5.3.0-B1]

The "Google Checkout" has ceased to exist in 20 November 2013 (see http://googlecommerce.blogspot.com/2013/05/an-update-to-google-checkout-for.html). From customer side it's been replaced with Google Wallet, but I'm not sure if same can be done for merchants.

I propose we delete Google Checkout related code from In-Commerce and if later a need arises to integrate Google Wallet, then we'll do that.

Development Team