I have ansible 2.4.2.x running and an inventory file which has "ansible_ssh_host etc." params.Normally ansible_ssh_host must be ansible_host as it is deprecated. deprecated .
when I play with ansible_host parameter I get this
"msg": "AnsibleUndefinedVariable: 'dict object' has no attribute 'ansible_ssh_host'"}
Here is the latest doc.It is "ansible_host" and no mention of deprecated anymore.ansible latest doc