Revert "Add ldap auth"

helios_auth/auth_systems/__init__.py

helios_auth/auth_systems/ldapauth.py

helios_auth/auth_systems/ldapbackend/__init__.py

helios_auth/auth_systems/ldapbackend/backend.py

helios_auth/media/login-icons/ldap.png

helios_auth/tests.py

helios_auth/urls.py

requirements.txt

settings.py