Revert "fix: use proper provider source for datadog"

This reverts commit 6f292e7.

- This change to be backed out of the v1 major release as it breaks
  support for Terraform 0.12.x

Author: jim80net

versions.tf

@@ -2,9 +2,6 @@ terraform {
   required_version = ">= 0.12, < 0.14"
 
   required_providers {
-    datadog = {
-      source  = "DataDog/datadog"
-      version = ">= 2.10, < 3"
-    }
+    datadog = ">= 2.10, < 3"
   }
 }