Remove grafana-cloud

I've migrated back to Uptime Robot, for simplicity. Sadly their API limits make it almost impossible to properly Terraform.

terraform/variables.tf

@@ -18,14 +18,6 @@ variable "gandi_api_key" {
   sensitive = true
 }
 
-variable "grafana_cloud_api_key" {
-  sensitive = true
-}
-
-variable "grafana_cloud_synthetic_monitoring_token" {
-  sensitive = true
-}
-
 variable "backblaze_application_key" {
   sensitive = true
 }