Remove nifcloud terraform provider support (it is no longer available) (#12936)

The nifcloud terraform provider has been deleted, so remove support and
CI.

contrib/terraform/nifcloud/variables.tf

@@ -1,77 +0,0 @@
-variable "region" {
-  description = "The region"
-  type        = string
-}
-
-variable "az" {
-  description = "The availability zone"
-  type        = string
-}
-
-variable "private_ip_bn" {
-  description = "Private IP of bastion server"
-  type        = string
-}
-
-variable "private_network_cidr" {
-  description = "The subnet of private network"
-  type        = string
-  validation {
-    condition     = can(cidrnetmask(var.private_network_cidr))
-    error_message = "Must be a valid IPv4 CIDR block address."
-  }
-}
-
-variable "instances_cp" {
-  type = map(object({
-    private_ip = string
-  }))
-}
-
-variable "instances_wk" {
-  type = map(object({
-    private_ip = string
-  }))
-}
-
-variable "instance_key_name" {
-  description = "The key name of the Key Pair to use for the instance"
-  type        = string
-}
-
-variable "instance_type_bn" {
-  description = "The instance type of bastion server"
-  type        = string
-}
-
-variable "instance_type_wk" {
-  description = "The instance type of worker"
-  type        = string
-}
-
-variable "instance_type_cp" {
-  description = "The instance type of control plane"
-  type        = string
-}
-
-variable "image_name" {
-  description = "The name of image"
-  type        = string
-}
-
-variable "working_instance_ip" {
-  description = "The IP address to connect to bastion server."
-  type        = string
-}
-
-variable "accounting_type" {
-  type    = string
-  default = "2"
-  validation {
-    condition = anytrue([
-      var.accounting_type == "1", // Monthly
-      var.accounting_type == "2", // Pay per use
-    ])
-    error_message = "Must be a 1 or 2."
-  }
-}