The code in optional_extension was mostly unused and is removed in this ticket (and similarly extension.skip_build was nowhere else set).
The only still used method was is_package_installed_and_updated which is moved to sage.misc.package.

Related: #28815

CC: @mkoeppe @kiwifb

Component: build

Keywords: sd111

Author: Tobias Diez

Branch/Commit: a7b1e81

Reviewer: François Bissey

Issue created by migration from https://trac.sagemath.org/ticket/31013