Remove obsolete methods from tempest service client

Commit https://github.com/openstack/manila/commit/2c7595a3
implemented "share servers" approach and removed Manila share-network
activation/deactivation APIs. Manila service client in Tempest plugin was not
updated with this API change and several redundant methods left.

Change-Id: Idd76fed790f8bfc9f7e3502e10dd130bbe5f5bfd