modernize super in root_systems

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using the short syntax `super()` where possible

Component: **combinatorics**

Author: **Frédéric Chapoton**

Branch/Commit: **[`512fcf8`](https://github.com/sagemath/sagetrac-mirror/commit/512fcf88770e4e434617bcc356500ee6aa2492dc)**

Reviewer: **Matthias Koeppe**

_Issue created by migration from https://trac.sagemath.org/ticket/34743_

