Remove default region from Terraform variable

Region is now always supplied via TF_VAR_region from the GitHub Actions
environment, so a default would silently mask a missing configuration.

https://claude.ai/code/session_016Vbi79bAso2hVJAj3nXEkM

Author: claude

packages/ping-home/terraform/variables.tf

@@ -1,2 +1,2 @@
 variable "project_id" { type = string }
-variable "region" { type = string, default = "europe-north1" }
+variable "region" { type = string }