[libkwineffects] Drop AniData constructor that receives QString

Summary:
This code has several bugs, it's untested, it's not used anywhere, it
adds unnecessary complexity -> delete it.

Test Plan: Compiles.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D16099