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/inputs.tf

@@ -31,14 +31,6 @@ variable "require_vpn_to_access" {
   default     = true
 }
 
-variable "codestar_connection_arn" {
-  description = "It isn't possible to automate the creation of a CodeStar connection, so we must create it by hand once in each account and hardcode its ARN."
-  type = object({
-    alphagov    = string
-    govuk-forms = string
-  })
-}
-
 variable "deploy_account_id" {
   description = "the account number for deploy account"
   type        = string

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 = {