Hide the Button of delete aggregate if a host in the aggregate

According to the code in [1], if there is a host in the aggregate,
an error will be shown when deleting.
[1]https://github.com/openstack/nova/blob/948d63c6dc190ef94041fbeaa30091358a33c484/nova/compute/api.py#L5420-L5423

This Patch hide the delete button if a host in the aggregate

Change-Id: I79c1e32b84fef00a242e1adf5d87531d3f407c34
Closes-Bug: #1829102