tests/eolian: remove eolian_decl test

Summary:
<q66> just remove decl.eo and remove the eolian_decl test; it's useless
<q66> the reason: it used to be testing some specific API, which got replaced with more generalized API that is now used everywhere in the tests, so that specific test no longer has a purpose

resolves some compile errors due to type conflicts

Reviewers: q66

Reviewed By: q66

Subscribers: cedric, committers

Tags: efl

Differential Revision: https://phab.enlightenment.org/D6773