Problem

FutureIface is deprecated. Scrooge is more powerful when used with finagle integration, and in that case, higher-kinded-types won't play its advantages. Scrooge generated code is growing which increases source compilation time, we should get rid of the unused parts.

Solution

Remove them from code-gen. In generated code, replace HKT/FutureIface with MethodPerEndpoint. Remove some deprecated builders in both scrooge-gen and finagle that require HKT as the parameter.

Differential Revision: https://phabricator.twitter.biz/D747744