Uniformize headline: noncommutative polynomials

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Component: **documentation**

Author: **Kwankyu Lee**

Branch/Commit: **[`6c34279`](https://github.com/sagemath/sagetrac-mirror/commit/6c34279634da03100c2bff5ef0480622119642a2)**

Reviewer: **Matthias Koeppe**

_Issue created by migration from https://trac.sagemath.org/ticket/34825_

