Decommission Skype 2015 On-Prem servers

I want to decommission our Skype On-Prem (2015) servers and cleanup AD from the RTC delegations and groups (RTC* and CS*). I've been following the guide: https://learn.microsoft.com/en-us/skypeforbusiness/hybrid/decommission-remove-on-prem

However, when doing step 1 of "Prepare to remove the Skype for Business deployment" and run the commands, the command Get-CsAudioTestServiceApplication returns an object. In step 2 there is no corresponding Remove-cmdlet, so we tried disabling it with the Set-cmdlet.

Moving on to "Remove your on-premises Skype for Business deployment", when getting to step 3 I run "Publish-CsTopology -FinalizeUninstall" but gets the following error.

Publish-CsTopology : Command execution failed: Cannot publish topology changes. Users or contacts are still homed on a pool that would be deleted. Move or remove the users or contacts before continuing.
At line:1 char:1
+ Publish-CsTopology -FinalizeUninstall
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [Publish-CsTopology], Inva
   lidOperationException
    + FullyQualifiedErrorId : ProcessingFailed,Microsoft.Rtc.Management.Deploy
   ment.PublishTopologyCmdlet

Running the command generates a html file with the result, where the same error can be found and the following suggestion:

"UserPoolInUseResolution: Consult your Skype for Business Server documentation to learn how to move or disable objects still homed on the pool. To find those objects, execute the following cmdLets: Get-CsUser, Get-CsExUmContact, Get-CsCommonAreaPhone, Get-CsAnalogDevice, Get-CsRgsWorkflow, Get-CsDialInConferencingAccessNumber, Get-CsAudioTestServiceApplication, Get-CsTrustedApplicationEndpoint, Get-CsPersistentChatEndpoint."

So I'm guessing we need to get rid of that Audio Test Service Application, anyone got any ideas how to do that? I can't find anything for it in the GUI either.

The main objective is to clean up any remnents in AD, the entire Skype environment will be removed and all servers decommissioned. I'm guessing that the Disable-CsAdDomain and Disable-CsAdForest cmdlets does this somewhat. Is the above steps a requirement to be able to run these cmdlets, or would this be a viable option?