eolian: remove legacy handling API and most of generation

eolian: remove legacy handling API and most of generation

Summary:
This removes all Eolian API that deals with handling of legacy
code. It also removes the code using it in the generator as well
as bindings, but for now keeps generation of .eo.legacy.h types,
as there are still instances in our codebase where things are
otherwise broken. We can remove the rest once that is resolved.

Reviewers: zmike, cedric

Subscribers: #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D8255