Remove obsolete field 'grouping' from environment

Field 'grouping' was removed from cluster DB model in Fuel. Remove this field
from EnvShow command class to avoid error with non-existent field.

Change-Id: I9684c125a36c6a9b6f2405fa4c0cdc915b5142a2
Closes-bug: 1483262

fuelclient/commands/environment.py

@@ -39,7 +39,6 @@ class EnvShow(EnvMixIn, base.BaseShowCommand):
                "status",
                "fuel_version",
                "name",
-               "grouping",
                "mode",
                "release_id",
                "pending_release_id",

fuelclient/tests/utils/fake_env.py

@@ -27,7 +27,6 @@ def get_fake_env(name=None, status=None, release_id=None,
             'is_customized': False,
             'release_id': release_id or 1,
             'name': name or 'fake_env',
-            'grouping': 'roles',
             'net_provider': 'neutron',
             'net_segment_type': 'gre',
             'fuel_version': fuel_version or '5.1',