Remove projects_prometheus_active from EE

ee/lib/ee/gitlab/usage_data.rb

@@ -309,7 +309,6 @@ module EE
         def usage_activity_by_stage_monitor(time_period)
           super.merge({
             operations_dashboard_users_with_projects_added: distinct_count(UsersOpsDashboardProject.joins(:user).merge(::User.active).where(time_period), :user_id),
-            projects_prometheus_active: distinct_count(::Project.with_active_prometheus_service.where(time_period), :creator_id),
             projects_incident_sla_enabled: count(::Project.with_enabled_incident_sla)
           })
         end

ee/spec/lib/ee/gitlab/usage_data_spec.rb

@@ -457,12 +457,10 @@ RSpec.describe Gitlab::UsageData do
 
       expect(described_class.usage_activity_by_stage_monitor({})).to include(
         operations_dashboard_users_with_projects_added: 2,
-        projects_prometheus_active: 2,
         projects_incident_sla_enabled: 2
       )
       expect(described_class.usage_activity_by_stage_monitor(described_class.last_28_days_time_period)).to include(
         operations_dashboard_users_with_projects_added: 1,
-        projects_prometheus_active: 1,
         projects_incident_sla_enabled: 2
       )
     end