refactor: Refactoring to match the rest of terraform-aws-modules (#1583)

examples/instance_refresh/variables.tf

@@ -1,18 +1,17 @@
-variable "region" {
-  default = "us-west-2"
-}
-
 variable "aws_node_termination_handler_chart_version" {
   description = "Version of the aws-node-termination-handler Helm chart to install."
+  type        = string
   default     = "0.15.0"
 }
 
 variable "namespace" {
   description = "Namespace for the aws-node-termination-handler."
+  type        = string
   default     = "kube-system"
 }
 
 variable "serviceaccount" {
   description = "Serviceaccount for the aws-node-termination-handler."
+  type        = string
   default     = "aws-node-termination-handler"
 }