Remove experimental flag from share groups feature

The share groups functionality will no longer be considered
experimental. The existent functional tests were modified to accomplish
with this feature graduation.

Change-Id: Ideba68c0481345e808f185195eea68e879155cf1
Partially-Implements: bp graduate-share-groups-feature
diff --git a/manila_tempest_tests/tests/api/base.py b/manila_tempest_tests/tests/api/base.py
index 22b1d72..8c18a4b 100644
--- a/manila_tempest_tests/tests/api/base.py
+++ b/manila_tempest_tests/tests/api/base.py
@@ -609,8 +609,7 @@
         if kwargs.get('source_share_group_snapshot_id'):
             new_share_group_shares = client.list_shares(
                 detailed=True,
-                params={'share_group_id': share_group['id']},
-                experimental=True)
+                params={'share_group_id': share_group['id']})
 
             for share in new_share_group_shares:
                 resource = {"type": "share",