clean whitespace W293 in py files

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but one, changed elsewhere

and in some pyx files too

Component: **refactoring**

Author: **Frédéric Chapoton**

Branch/Commit: **[`ae432e3`](https://github.com/sagemath/sagetrac-mirror/commit/ae432e3ffc5e2464021f4e0d96e6d060d57468ec)**

Reviewer: **Matthias Koeppe**

_Issue created by migration from https://trac.sagemath.org/ticket/34704_

