remove deprecated diff. forms

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

following #24444

CC:  @egourgoulhon @tscrim @mwageringel

Component: **geometry**

Author: **Frédéric Chapoton**

Branch/Commit: **[`b63acc3`](https://github.com/sagemath/sagetrac-mirror/commit/b63acc36c732ca66bbb2250fed57c0fc29a5c133)**

Reviewer: **Travis Scrimshaw**

_Issue created by migration from https://trac.sagemath.org/ticket/32313_

