replace PyCrypto usage w/ crytography; ansible no longer bundles it

see: https://github.com/ansible/ansible-tower/issues/7395

tox.ini

@@ -11,8 +11,6 @@ envlist =
 basepython = python2.7
 setenv =
     DJANGO_SETTINGS_MODULE = awx.settings.development_quiet
-    # For OS X to be able to install pycrypto.
-    # CFLAGS = -I/opt/local/include
     SWIG_FEATURES = -cpperraswarn -includeall -I/usr/include/openssl
     HOME = {homedir}
     USERPROFILE = {homedir}