[v2] Service client removals (#9802)

* Remove qldb

* Remove robomaker

* Remove lookoutmetrics

* Remove lookoutvision

* Remove dlbq session

* Remove iotfleethub

* Remove apptest

* Changelog entry

---------

Co-authored-by: Andrew Asseily <[email protected]>

Author: hssyoo

.changes/next-release/api-change-clients-50666.json

@@ -0,0 +1,5 @@
+{
+  "type": "api-change",
+  "category": "clients",
+  "description": "The following clients have been removed per deprecation of the services - qldb, qldbsession, robomaker, lookoutmetrics, lookoutvision, iotfleethub, apptest"
+}