bpo-41685: Don't pin setuptools version anymore in Doc/Makefile (pythonGH-22062)

setuptools 50.0.2 is now compatible with Python 3.10:
pypa/setuptools#2361

Author: vstinner

Doc/Makefile

@@ -142,8 +142,7 @@ clean:
 
 venv:
 	$(PYTHON) -m venv $(VENVDIR)
-#	$(VENVDIR)/bin/python3 -m pip install -U pip setuptools
-	$(VENVDIR)/bin/python3 -m pip install -U pip setuptools==49.2.1
+	$(VENVDIR)/bin/python3 -m pip install -U pip setuptools
 	$(VENVDIR)/bin/python3 -m pip install -U Sphinx==3.2.1 blurb python-docs-theme
 	@echo "The venv has been created in the $(VENVDIR) directory"