Usage ping counts service template in "projects_prometheus_active"

Summary

Here we calculate the value of projects_prometheus_active. This value includes a service template for Prometheus service. As a result, we send usage ping where projects_prometheus_active is sometimes greater (by 1) than projects. It's even possible that there are 0 projects but 1 projects_prometheus_active.

This skews the calculations in version.gitlab.com that we perform to obtain ConvDev Index score.