Removes hardcoded includes of prod-specific.yml file
Removes hardcoded includes of prod-specific.yml file

The production playbook was including the `prod-specific.yml` vars file
on every play, since previously the project did not leverage Ansible
group_vars in order to override role defaults.

conorsch/securedrop,garrettr/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,micahflee/securedrop,ageis/securedrop,micahflee/securedrop,ehartsuyker/securedrop,ageis/securedrop,conorsch/securedrop,garrettr/securedrop,heartsucker/securedrop,ageis/securedrop,ageis/securedrop,ehartsuyker/securedrop,conorsch/securedrop,garrettr/securedrop,ehartsuyker/securedrop,garrettr/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,micahflee/securedrop,conorsch/securedrop,ehartsuyker/securedrop,conorsch/securedrop,heartsucker/securedrop,micahflee/securedrop,heartsucker/securedrop