Require provider api_key and remove env var fallback

examples/read_only/providers.tf

@@ -12,7 +12,6 @@ terraform {
 # This source address stays "dynu/dynu" while using ~/.terraformrc dev_overrides.
 # Terraform will load your local terraform-provider-dynu binary instead of the public registry.
 provider "dynu" {
-  # Use DYNU_API_KEY environment variable by default.
-  # Set var.dynu_api_key in terraform.tfvars to override.
+  # Set var.dynu_api_key in terraform.tfvars.
   api_key = var.dynu_api_key
 }

examples/read_only/terraform.tfvars.example

@@ -1,6 +1,5 @@
 # Copy to terraform.tfvars and adjust values for your environment.
-# dynu_api_key can be omitted when DYNU_API_KEY is exported in your shell.
-# dynu_api_key = "replace-with-dynu-api-key"
+dynu_api_key = "replace-with-dynu-api-key"
 
 # Use a hostname that exists in your Dynu account.
 hostname = "www.example.com"

examples/read_only/variables.tf

@@ -1,5 +1,5 @@
 variable "dynu_api_key" {
-  description = "Dynu API key. Leave null to use DYNU_API_KEY from environment."
+  description = "Dynu API key used by the provider. Set in terraform.tfvars."
   type        = string
   default     = null
   sensitive   = true