Get rid of _param:influxdb_password

This parameter and influxdb_stacklight_password are redundant and they
have to be set to the same value.
diff --git a/grafana/client/single.yml b/grafana/client/single.yml
index c36d4ff..1197ef3 100644
--- a/grafana/client/single.yml
+++ b/grafana/client/single.yml
@@ -18,6 +18,6 @@
           host: ${_param:grafana_influxdb_host}
           port: ${_param:influxdb_port}
           user: ${_param:influxdb_user}
-          password: ${_param:influxdb_password}
+          password: ${_param:influxdb_stacklight_password}
           database: ${_param:influxdb_database}
           is_default: true