Get rid of _param:influxdb_database

The StackLight database in InfluxDB is set to 'lma' by default. If one
wants to override it, it should be done in the user model.
diff --git a/grafana/client/single.yml b/grafana/client/single.yml
index 35704a8..49ac876 100644
--- a/grafana/client/single.yml
+++ b/grafana/client/single.yml
@@ -19,5 +19,5 @@
           port: ${_param:influxdb_port}
           user: lma
           password: ${_param:influxdb_stacklight_password}
-          database: ${_param:influxdb_database}
+          database: lma
           is_default: true