Eliminate direct use of os.getenv in sage.interfaces #33405
Description
... as shown by git grep getenv, environment variables such as SAGE_MACAULAY2_COMMAND are checked.
These should go through variables defined in sage.env (and perhaps through sage.feature, Executable.absolute_filename(), #31296) so that they can be configured using sage_conf as well.
(see also #32867 comment:31 to #32867 comment:36)
See also: #32957 Replace have_program usage by Features
- Depends on sage.features.Executable: Prepend $SAGE_VENV/bin:$SAGE_LOCAL/bin to PATH #31296
- Depends on FriCAS spkg-configure and Feature #35838
CC: @kiwifb @antonio-rojas @fchapoton @orlitzky @tornaria @dimpase
Component: refactoring
Issue created by migration from https://trac.sagemath.org/ticket/33405