Remove code that was blocking the builders due to a solved pip issue

Makefile

@@ -165,7 +165,6 @@ clean-staticdeps:
 staticdeps: clean-staticdeps
 	test "${SKIP_PY_CHECK}" = "1" || python2 --version 2>&1 | grep -q 2.7 || ( echo "Only intended to run on Python 2.7" && exit 1 )
 	pip2 install -t kolibri/dist -r "requirements.txt"
-	rm -rf kolibri/dist/*.dist-info  # pip installs from PyPI will complain if we have more than one dist-info directory.
 	rm -rf kolibri/dist/*.egg-info
 	rm -r kolibri/dist/man kolibri/dist/bin || true # remove the two folders introduced by pip 10
 	python2 build_tools/py2only.py # move `future` and `futures` packages to `kolibri/dist/py2only`
@@ -175,8 +174,6 @@ staticdeps-cext:
 	rm -rf kolibri/dist/cext || true # remove everything
 	python build_tools/install_cexts.py --file "requirements/cext.txt" # pip install c extensions
 	pip install -t kolibri/dist/cext -r "requirements/cext_noarch.txt" --no-deps
-	rm -rf kolibri/dist/*.dist-info  # pip installs from PyPI will complain if we have more than one dist-info directory.
-	rm -rf kolibri/dist/cext/*.dist-info  # pip installs from PyPI will complain if we have more than one dist-info directory.
 	rm -rf kolibri/dist/*.egg-info
 	make test-namespaced-packages
 

requirements/build.txt

@@ -3,6 +3,7 @@
 # This does not depend on runtime stuff so we do not
 # include base.txt
 pex<1.6
+pip>=20.1
 setuptools>=20.3,<41,!=34.*,!=35.*  # https://github.com/pantsbuild/pex/blob/master/pex/version.py#L6 # pyup: ignore
 beautifulsoup4==4.8.2
 requests==2.21.0