Drop support for Ogone and Authorize.net

We are dropping support for Ogone and Authorize.net payment gateways.  We need to:

1. Remove them from SaaS for customers not using them.

   Ogone and Authorize.net not listed in credit card gateway dropdown. (Admin portal -> Settings -> Billing)

2. Continue to support existing customers.

   Existing customers using one of these gateways will continue having the selected option.

3. Update documentation for Ogone and Authorize.net

   Docs for Ogone and Authorize.net should be removed from the menu structure but not deleted (See subtask THREESCALE-1064)

Note that we are also dropping support from on-premises. See THREESCALE-1061