evas: make efl_canvas_animation abstract

it seems that this class does not have a meaning when created just like
this. Other classes using it are even abstract, which means, this class
should also be abstract. This is done in order to support that a
abstract class should only contain abstract

ref T7240

Reviewed-by: Xavi Artigas <xavierartigas@yahoo.es>
Reviewed-by: Cedric BAIL <cedric.bail@free.fr>
Differential Revision: https://phab.enlightenment.org/D7601

src/lib/evas/canvas/efl_canvas_animation.eo

@@ -1,6 +1,6 @@
 import efl_canvas_animation_types;
 
-class Efl.Canvas.Animation (Efl.Object, Efl.Playable)
+abstract Efl.Canvas.Animation (Efl.Object, Efl.Playable)
 {
    [[Efl animation class]]
    eo_prefix: efl_animation;