Use Tempest-lib's aggregate client

Aggregate service client has been migrated to tempest-lib-
Ia20fd3914aa6e5ac829bfd3fb88bb4f654958b53

Now Tempest-lib provides this client as stable interface so Tempest
should start using this from lib and remove its own copy.
Also remove other files for this client like response schema, unit tests.

This commits makes Tempest to use aggregate client from Tempest-lib.

Change-Id: I238c688beff26f63e804ebe86101205eb2c0c57c
Depends-on: I516d4119fd200c79a8be4598cbb0d732344e8b75
5 files changed