Update to use is_email_simple from django.util
Update to use is_email_simple from django.util

Reflects change in https://github.com/django/django/commit/8618271caa0b09daba39ff3b46567d33ae1e1d3a#diff-89d6614a06443d1da77f7fed3de3200c
tBaxter/tango-shared-core,tBaxter/tango-shared-core,tBaxter/tango-shared-core