group_vars: remove useless dashboard files

The only useful ansible group for the grafana/prometheus stack is
grafana-server so no one of those files are actually needed.
The default values for all dashboard roles are present in ceph-defaults
role so it's also present in in group_vars/all.yml.
Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>
(cherry picked from commit ec56a950)

group_vars/dashboards.yml.sample

----
-# Variables here are applicable to all host groups NOT roles
-
-# This sample file generated by generate_group_vars_sample.sh
-
-# Dummy variable to avoid error because ansible does not recognize the
-# file as a good configuration file when no variable in it.
-dummy:
-
-#dashboard_admin_user: admin
-#dashboard_admin_password: admin
-# We only need this for SSL (https) connections
-#dashboard_crt: ''
-#dashboard_key: ''
-#dashboard_rgw_api_user_id: ceph-dashboard
-#dashboard_rgw_api_host: ''
-#dashboard_rgw_api_port: ''
-#dashboard_rgw_api_scheme: ''
-#dashboard_rgw_api_admin_resource: ''
-#dashboard_rgw_api_no_ssl_verify: False
-#grafana_server_group_name: grafana-server

group_vars/grafanas.yml.sample

----
-# Variables here are applicable to all host groups NOT roles
-
-# This sample file generated by generate_group_vars_sample.sh
-
-# Dummy variable to avoid error because ansible does not recognize the
-# file as a good configuration file when no variable in it.
-dummy:
-
-#grafana_admin_user: admin
-#grafana_admin_password: admin
-# We only need this for SSL (https) connections
-#grafana_crt: ''
-#grafana_key: ''
-#grafana_container_image: "grafana/grafana:latest"
-#grafana_container_cpu_period: 100000
-#grafana_container_cpu_cores: 2
-# container_memory is in GB
-#grafana_container_memory: 4
-#grafana_uid: 472
-#grafana_datasource: Dashboard
-#grafana_dashboards_path: "/etc/grafana/dashboards/ceph-dashboard"
-#grafana_plugins:
-#  - vonage-status-panel
-#  - grafana-piechart-panel
-

group_vars/node-exporters.yml.sample

----
-# Variables here are applicable to all host groups NOT roles
-
-# This sample file generated by generate_group_vars_sample.sh
-
-# Dummy variable to avoid error because ansible does not recognize the
-# file as a good configuration file when no variable in it.
-dummy:
-
-#node_exporter_container_image: prom/node-exporter:latest
-

group_vars/prometheuss.yml.sample

----
-# Variables here are applicable to all host groups NOT roles
-
-# This sample file generated by generate_group_vars_sample.sh
-
-# Dummy variable to avoid error because ansible does not recognize the
-# file as a good configuration file when no variable in it.
-dummy:
-
-#prometheus_container_image: prom/prometheus:latest
-#prometheus_container_cpu_period: 100000
-#prometheus_container_cpu_cores: 2
-# container_memory is in GB
-#prometheus_container_memory: 4
-#prometheus_data_dir: /var/lib/prometheus
-#prometheus_conf_dir: /etc/prometheus
-#prometheus_user_id: '65534'  # This is the UID used by the prom/prometheus container image
-
-#alertmanager_container_image: prom/alertmanager:latest
-#alertmanager_container_cpu_period: 100000
-#alertmanager_container_cpu_cores: 2
-# container_memory is in GB
-#alertmanager_container_memory: 4
-#alertmanager_data_dir: /var/lib/alertmanager
-#alertmanager_conf_dir: /etc/alertmanager
-