Remove CodeBuild runner infrastructure

Remove the CodeBuild-hosted GitHub Actions runner infrastructure now
that review apps use GitHub-hosted runners with OIDC authentication.

The gha-runner module and CodeBuild resources are no longer needed.

Author: whi-tw

infra/deployments/integration/review/gha-runner/inputs.tf

@@ -1,4 +1,5 @@
 data "aws_region" "current" {}
+data "aws_caller_identity" "current" {}
 
 locals {
   github_actions_apps = {