For a long time now, the Makefile ensures that packages are automatically reinstalled when the version in build/pkgs/SPKG/package-version.txt changes.

Thus we now remove the check whether the installed package version is current from sage.doctest.control and sage_setup (ex OptionalExtension code).

This simplifies the code, and in particular removes the direct reading of build/pkgs/ from sagelib.

CC: @dimpase @jhpalmieri @kiwifb

Component: build

Keywords: sd111

Branch: u/mkoeppe/sage_doctest_control__sage_setup__do_not_check_versions_of_installed_packages

Issue created by migration from https://trac.sagemath.org/ticket/30848