On-prem docs should not include hosted APIcast SaaS and SaaS docs shouldn't include built-in APIcast

APIcast docs in SaaS include references to APIcast built-in, which really does not exist in SaaS (equivalent would be hosted APIcast).

The same way, APIcast docs in 2.3 (and I guess previous ones too?) include references to APIcast hosted, which is not available in on-premises. In this case, it should only talk about built-in addition to self-managed.

There are 3 references
1) needs to be removed

2) in 1.3 it needs to be changed by 'built-in'

3) APIcast hosted section https://access.redhat.com/documentation/en-us/red_hat_3scale/2.3/html/deployment_options/apicast-hosted
The way staging and production works is similar in APIcast hosted (SaaS) / built-in APIcast (onprem) but there's no APIcast hosted in on-onpremises. e.g. policies available are different, customizations not possible, etc. Since these topics are not covered in section 2 in APIcast > Deployment options we could potentially leave the content as is just change 'hosted' by 'built-in'.