Removing unused admin_client

After the merger of blueprint 'modifying-switching-role-mechanism',
no admin_client is needed.
As a part part of cleanup, this patch aims to remove unused admin_client.

Partially implements: blueprint cleanup-as-a-result-of-framework-change

Change-Id: I576bc2319d6d621443f816765e9b6ff2ae739f8a
8 files changed