Fix an error in API reference for receiver list
Fix an error in API reference for receiver list

This patch fixes an error in API reference for receiver
list: `user` is not a valid query parameter for receiver
list API.

Change-Id: If032eaa5961604c5ec10935f0703264e8358b95d

stackforge/senlin,stackforge/senlin,openstack/senlin,openstack/senlin,openstack/senlin