Revert "Bump min setuptools version and remove setup.py (FEniCS#154)"

This reverts commit 6eeef93.

Numpy currently pins setuptools to 59.2 see:
numpy/numpy#22623

This commit caused UFL to require a lated setuptools. For complex
reasons to do with blas dependencies, Firedrake builds numpy without
build isolation. We also install UFL in editable mode, so that can't
use build isolation. Consequently we are stuck on the pinned setuptools.

pyproject.toml

@@ -1,4 +1,4 @@
 [build-system]
-requires = ["setuptools>=62", "wheel"]
+requires = ["setuptools>=58", "wheel"]
 
 build-backend = "setuptools.build_meta"

setup.cfg

@@ -39,7 +39,7 @@ include_package_data = True
 zip_safe = False
 python_requires = >= 3.8
 setup_requires =
-    setuptools >= 62
+    setuptools >= 58
     wheel
 install_requires =
     numpy

setup.py

@@ -0,0 +1,16 @@
+import setuptools
+
+try:
+    import pip
+
+    from packaging import version
+    if version.parse(pip.__version__) < version.parse("21.3"):
+        # Issue with older version of pip https://github.com/pypa/pip/issues/7953
+        import site
+        import sys
+        site.ENABLE_USER_SITE = "--user" in sys.argv[1:]
+
+except ImportError:
+    pass
+
+setuptools.setup()