Change InfluxDB interface from Flux to InfluxQL

It's mentioned how to set it in the third provisioning example here:
https://grafana.com/docs/grafana/latest/datasources/influxdb/#provisioning-examples

The Flux language is so bad it's been deprecated before it's even supported by Grafana properly.  
The InfluxQL language is much more friendly because the Grafana UI builds the queries for you.