##### SUMMARY
Removing a cron_file is no longer possible since 2.8 without specifying the user parameter.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
cron

##### ANSIBLE VERSION
```paste below
ansible 2.8.1
  config file = /home/duck/OSPO/community-cage-infra-ansible/ansible.cfg
  configured module search path = ['/home/duck/OSPO/community-cage-infra-ansible/library']
  ansible python module location = /home/duck/.local/lib/python3.7/site-packages/ansible
  executable location = /home/duck/.local/bin/ansible
  python version = 3.7.3 (default, Apr  3 2019, 05:39:12) [GCC 8.3.0]
```

##### CONFIGURATION
```paste below
ANSIBLE_FORCE_COLOR(env: ANSIBLE_FORCE_COLOR) = True
ANSIBLE_PIPELINING(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = True
ANSIBLE_SSH_ARGS(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = -o ControlMaster=auto -o ControlPersist=30m
CACHE_PLUGIN(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = jsonfile
CACHE_PLUGIN_CONNECTION(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = ./facts_cache
CACHE_PLUGIN_TIMEOUT(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = 86400
DEFAULT_ACTION_PLUGIN_PATH(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = ['/home/duck/OSPO/community-cage-infra-ansible/plugins/actio
DEFAULT_CALLBACK_PLUGIN_PATH(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = ['/home/duck/OSPO/community-cage-infra-ansible/plugins/cal
DEFAULT_CONNECTION_PLUGIN_PATH(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = ['/home/duck/OSPO/community-cage-infra-ansible/plugins/c
DEFAULT_FILTER_PLUGIN_PATH(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = ['/home/duck/OSPO/community-cage-infra-ansible/plugins/filte
DEFAULT_FORKS(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = 10
DEFAULT_GATHERING(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = smart
DEFAULT_HASH_BEHAVIOUR(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = merge
DEFAULT_HOST_LIST(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = ['/home/duck/OSPO/community-cage-infra-ansible/hosts.yml']
DEFAULT_LOOKUP_PLUGIN_PATH(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = ['/home/duck/OSPO/community-cage-infra-ansible/plugins/looku
DEFAULT_MANAGED_STR(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = Ansible managed
DEFAULT_MODULE_PATH(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = ['/home/duck/OSPO/community-cage-infra-ansible/library']
DEFAULT_ROLES_PATH(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = ['/home/duck/OSPO/community-cage-infra-ansible/roles']
DEFAULT_STRATEGY_PLUGIN_PATH(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = ['/home/duck/OSPO/community-cage-infra-ansible/plugins/str
DEFAULT_TIMEOUT(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = 40
DEFAULT_VARS_PLUGIN_PATH(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = ['/home/duck/OSPO/community-cage-infra-ansible/plugins/vars']
DEFAULT_VAULT_PASSWORD_FILE(env: ANSIBLE_VAULT_PASSWORD_FILE) = /home/duck/.ansible_vault/cage.txt
ERROR_ON_MISSING_HANDLER(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = True
PARAMIKO_HOST_KEY_AUTO_ADD(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = True
PERSISTENT_CONNECT_TIMEOUT(/home/duck/OSPO/community-cage-infra-ansible/ansible.cfg) = 1800
```

##### OS / ENVIRONMENT
Ansible runs on Debian unstable and the node is using Debian Stretch.

##### STEPS TO REPRODUCE
The following worked before 2.8 and now fails.

```yaml
- name: remove useless backup cron
  cron:
    cron_file: backup-postgresql-databases
    state: absent
```

##### EXPECTED RESULTS

There is no reason to request the user when deleting the contab file thus it should continue to work as before 2.8.

I would dare to say a test is missing here.

##### ACTUAL RESULTS

```paste below
fatal: [catton.osci.io]: FAILED! => {"changed": false, "msg": "missing parameter(s) required by 'cron_file': user"}
```

return "%s%s" % (self.ansible, name)
    def add_job(self, name, job):
        
        self.lines.append(self.do_comment(name))
        
        self.lines.append("%s" % (job))
    def update_job(self, name, job):