Remove useless check in _add_retry_host

In populate_retry, the code already check the case with force_hosts
and force_nodes. (https://github.com/openstack/nova/blob/418398dcca5
52497c8488dbbf54a06e21202b295/nova/scheduler/utils.py#L134)
If the retry is disable, populate_retry won't add retry info into
filter_properties.

_add_retry_host is called later than populate_retry. It also check
the force_hosts and force_nodes, that is useless. (https://github.com
/openstack/nova/blob/418398dcca552497c8488dbbf54a06e21202b295/nova/
scheduler/utils.py#L193) It only need check whether retry info exist
in filter_properties or not.

Change-Id: I1f83b4b584d36aa6f894180d43aee24f096b4f78
Merge "Remove useless check in _add_retry_host"