Revert "build/bin/sage-dist-helpers (sdh_pip_editable_install), build/pkgs/sagelib/spkg-install: Do not use PEP 660 editable wheels"

This reverts commit a292013.

Author: Matthias Koeppe

build/bin/sage-dist-helpers

@@ -290,8 +290,6 @@ sdh_pip_install() {
 
 sdh_pip_editable_install() {
     echo "Installing $PKG_NAME (editable mode)"
-    # Until https://trac.sagemath.org/ticket/34209 switches us to PEP 660 editable wheels
-    export SETUPTOOLS_ENABLE_FEATURE=legacy-editable
     python3 -m pip install --verbose --no-deps --no-index --no-build-isolation --isolated --editable "$@" || \
         sdh_die "Error installing $PKG_NAME"
 }

build/pkgs/sagelib/spkg-install

@@ -52,8 +52,6 @@ if [ "$SAGE_EDITABLE" = yes ]; then
     # and renamed the distribution to "sagemath-standard").  There is no clean way to uninstall
     # them, so we just use rm.
     (cd "$SITEPACKAGESDIR" && rm -rf sage sage_setup sage-[1-9]*.egg-info sage-[1-9]*.dist-info)
-    # Until https://trac.sagemath.org/ticket/34209 switches us to PEP 660 editable wheels
-    export SETUPTOOLS_ENABLE_FEATURE=legacy-editable
     time python3 -m pip install --verbose --no-deps --no-index --no-build-isolation --isolated --editable . || exit 1
 else
     # Make sure that an installed old version of sagelib in which sage is an ordinary package