Removed custom WSGIRequestHandler.get_environ

We probably historically customized it for good reasons, but
currently, the differences with upstream Python are not
significant any longer.
Also fixes #19075 for which a test has been added.

tests/regressiontests/servers/views.py

@@ -14,4 +14,8 @@ def model_view(request):
 def create_model_instance(request):
     person = Person(name='emily')
     person.save()
-    return HttpResponse('')
+    return HttpResponse('')
+
+
+def environ_view(request):
+    return HttpResponse("\n".join(["%s: %r" % (k, v) for k, v in request.environ.items()]))