some care for trailing whitespaces

<div id="comment:0"></div>

pycodestyle W2 and W3

here both in some py and pyx files

Component: **refactoring**

Author: **Frédéric Chapoton**

Branch/Commit: **[`ca00c97`](https://github.com/sagemath/sagetrac-mirror/commit/ca00c97bc3c4beee54c28157634a919d4b7eebb5)**

Reviewer: **Matthias Koeppe**

_Issue created by migration from https://trac.sagemath.org/ticket/34672_

