Remove add_placement_groups from tests (linode#597)

Author: zliang-akamai

test/unit/objects/account_test.py

@@ -379,7 +379,6 @@ def test_user_grants_serialization():
             "add_linodes": True,
             "add_longview": True,
             "add_nodebalancers": True,
-            "add_placement_groups": True,
             "add_stackscripts": True,
             "add_volumes": True,
             "add_vpcs": True,