this is a follow-up of #15076

and a step towards #14329

Apply:

• attachment: trac_15098_remove_global_is_in_matrix.patch
• attachment: trac_15098_review-dg.patch​

Depends on #15076

Component: linear algebra

Keywords: deprecation cleanup

Author: Frédéric Chapoton

Reviewer: Darij Grinberg

Merged: sage-5.13.beta3

Issue created by migration from https://trac.sagemath.org/ticket/15098