CI: Drop install_extras, remove hack from env.sh

Also bring setuptools requirement in line with pyproject.toml

setup.py

@@ -6,9 +6,9 @@
 import versioneer
 
 # Give setuptools a hint to complain if it's too old a version
-# 30.3.0 allows us to put most metadata in setup.cfg
+# 40.8 allows us to put most metadata in setup.cfg
 # Should match pyproject.toml
-SETUP_REQUIRES = ['setuptools >= 30.3.0']
+SETUP_REQUIRES = ['setuptools >= 40.8']
 # This enables setuptools to install wheel on-the-fly
 SETUP_REQUIRES += ['wheel'] if 'bdist_wheel' in sys.argv else []
 

tools/ci/env.sh

@@ -1,11 +1,6 @@
-SETUP_REQUIRES="pip setuptools>=30.3.0 wheel"
+SETUP_REQUIRES="pip setuptools>=40.8 wheel"
 
 # Numpy and scipy upload nightly/weekly/intermittent wheels
 NIGHTLY_WHEELS="https://pypi.anaconda.org/scipy-wheels-nightly/simple"
 STAGING_WHEELS="https://pypi.anaconda.org/multibuild-wheels-staging/simple"
 PRE_PIP_FLAGS="--pre --extra-index-url $NIGHTLY_WHEELS --extra-index-url $STAGING_WHEELS"
-
-# XXX This is necessary to deal with scipy version metadata mismatches
-# We should aim to remove this ASAP.
-# Last check: 2020.12.19
-PRE_PIP_FLAGS="--use-deprecated=legacy-resolver $PRE_PIP_FLAGS"