Remove conductor_api and _last_host_check from manager.py
Remove conductor_api and _last_host_check from manager.py

conductor_api and _last_host_check are not
used in manager.py, so this is to remove them.

Part of blueprint remove-cells-v1

Change-Id: I9f52b84e00c92d7734690d115e2b5e8f9c788f15

mahak/nova,rahulunair/nova,klmitch/nova,klmitch/nova,klmitch/nova,rahulunair/nova,openstack/nova,klmitch/nova,openstack/nova,openstack/nova,rahulunair/nova,mahak/nova,mahak/nova