ecore_audio: remove pure virtual functions from classes
Summary:
A call to a undefined function results in a NOP we can get the same
behaviour with @empty. In Ecore.Audio this pure_virtual function makes
sense, so make the class abstract.
ref T7632
Reviewers: cedric, segfaultxavi, zmike, q66
Reviewed By: segfaultxavi
Subscribers: reviewers, committers
Tags: efl
Maniphest Tasks: T7632
Differential Revision: https://phab.enlightenment.org/D7669