feat!: remove support for dashboards v1 and v2

Author: tembleking

examples/dashboard_backup_v1_restore_v2.py

@@ -1,11 +1,9 @@
-from ._dashboards_v2 import DashboardsClientV2
 from ._dashboards_v3 import DashboardsClientV3
 from ._events_v1 import EventsClientV1
 from ._events_v2 import EventsClientV2
 
 __all__ = [
     "DashboardsClientV3",
-    "DashboardsClientV2",
     "EventsClientV1",
     "EventsClientV2",
 ]