Inline inherited interfaces to work around gomock bugs.

gomock can't handle cross-package interfaces for some reason, so this patch changes thrift to inline inherited interfaces. Because of how Go inheritance works this *should* have no actual semantic changes.

Sample diff of generated code:

```
 type ApiTokens interface {
-       base_service.BaseService
-
+       // Parameters:
+       //  - DropFirst
+       ResetTestDatabase(drop_first bool) (e *types.ServiceException, err error)
```