Revert "Add support for building/testing w/ 'PURE_PYTHON' defined."

setup.py

@@ -79,12 +79,11 @@ def _unavailable(self, e):
     py_impl = getattr(platform, 'python_implementation', lambda: None)
     is_pypy = py_impl() == 'PyPy'
     is_jython = 'java' in sys.platform
-    is_pure = 'PURE_PYTHON' in os.environ
 
     # Jython cannot build the C optimizations, while on PyPy they are
     # anti-optimizations (the C extension compatibility layer is known-slow,
     # and defeats JIT opportunities).
-    if is_pypy or is_jython or is_pure:
+    if is_pypy or is_jython:
         features = {}
     else:
         features = {'codeoptimization': codeoptimization}

tox.ini

@@ -1,23 +1,13 @@
 [tox]
 envlist =
-    py27,py27-pure,py33,py34,py34-pure,py35,pypy,pypy3,coverage,docs
+    py27,py33,py34,py35,pypy,pypy3,coverage,docs
 
 [testenv]
 commands =
     python setup.py -q test -q
 deps =
     zope.event
 
-[testenv:py27-pure]
-setenv =
-    PURE_PYTHON=1
-    PIP_CACHE_DIR = {envdir}/.cache
-
-[testenv:py34-pure]
-setenv =
-    PURE_PYTHON=1
-    PIP_CACHE_DIR = {envdir}/.cache
-
 [testenv:py]
 commands =
     python --version