efl-csharp: Fix event callback removal.
Summary:
Use the native event loaded from dlsym directly instead of wrapping it
in a Event_Description structure.
Fixes: T7355
Reviewers: felipealmeida, vitor.sousa, segfaultxavi
Reviewed By: vitor.sousa
Subscribers: cedric, reviewers, committers
Tags: efl: language bindings
Differential Revision: https://phab.enlightenment.org/D6981