Refactor: using the split-out auth package

[tombuildsstuff]

Switching over to using the new github.com/hashicorp/go-azure-helpers package now that it's split out

Once this is merged I'll send a follow up to update existing calls to the (now) deprecated package in ./azurerm/helpers/response

[katbyte]

LGTM 🤖🚀

[tombuildsstuff]

Tests pass:

$ acctests azurerm TestAccAzureRMEnsureRequiredResourceProvidersAreRegistered
=== RUN   TestAccAzureRMEnsureRequiredResourceProvidersAreRegistered
...
--- PASS: TestAccAzureRMEnsureRequiredResourceProvidersAreRegistered (6.75s)
PASS
ok  	github.com/terraform-providers/terraform-provider-azurerm/azurerm	7.910s

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. If you feel I made an error 🤖 🙉 , please reach out to my human friends 👉 hashibot-feedback@hashicorp.com. Thanks!