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

Author: zhufl

nova/compute/manager.py

@@ -496,13 +496,11 @@ def __init__(self, compute_driver=None, *args, **kwargs):
         self.network_api = network.API()
         self.volume_api = cinder.API()
         self.image_api = image.API()
-        self._last_host_check = 0
         self._last_bw_usage_poll = 0
         self._bw_usage_supported = True
         self._last_bw_usage_cell_update = 0
         self.compute_api = compute.API()
         self.compute_rpcapi = compute_rpcapi.ComputeAPI()
-        self.conductor_api = conductor.API()
         self.compute_task_api = conductor.ComputeTaskAPI()
         self.is_neutron_security_groups = (
             openstack_driver.is_neutron_security_groups())