Removing SSRS Scale-Out Deployment Servers.. when the Config UI just won't do it

I am currently working on a TFS Upgrade.  We're going from an older TFS 2010 (that I think started life as something earlier than that) up to TFS 2013 (Update 3!).   We're following the ALM Ranger guidance and doing a Migration-based upgrade.  We've got a shiny new SQL Server 2014 with SSRS installed and it's time to migrate the old Reporting database over to the new hardware.  I've taken my backup from the old machines, and restored them to the new machines, then it's on to the SSRS Configuration manager to change databases over.. no troubles.. restore the old Encryption Key... and...  ahh, we find that the SSRS Server gives me this dreaded message when I try to view it:

Yes, when I changed databases, it brought over the old server to put in the Scale-Out deployment setting.  No trouble! I can go in to the Scale Out Deployment settings through SSRS Configuration Manager and Remove the un-needed server(s)!  Except, no, I can't.. it fails to remove them.  The old SSRS installation is SQL 2008R2, and I don't think my shiny new SQL 2014 server is up to the task of communicating quite perfectly.. I see this when I try to remove one of the old servers from my Scale-Out Deployment "Removing report server <instance id Guid> from the web farm of the local instance.   --- The task failed". Great!

When looking in the Tell me more about this problem link I get some details like this:

Microsoft.ReportingServices.WmiProvider.WMIProviderException: No report servers were found. ---> System.Management.ManagementException: Invalid namespace

   at System.Management.ManagementException.ThrowWithExtendedInfo(ManagementStatus errorCode)

   at System.Management.ManagementScope.InitializeGuts(Object o)

   at System.Management.ManagementScope.Initialize()

   at System.Management.ManagementScope.Connect()

   at ReportServicesConfigUI.WMIProvider.RSInstances.GetInstances(String machineName)

   --- End of inner exception stack trace ---

Well I HAVE to get it out of there somehow!  A little research, and a lot of asking for help, and a tip comes that I should try to use the command line to get that done.

Reading the MSDN Page Add and Remove Encryption Keys for Scale Out Deployment gets me what I need:

You can get the <installation ID> part of that from logging in to the machine you want to remove, and finding it in the rsreportserver.config file.  Or, WAY more easily, the error screen on the Configuration Manager when I tried to remove server also provides the Instance ID for me! 

Logging in to the SSRS Server, firing up the command prompt and running the command gave me no troubles.  The servers were removed from my Scale-Out Deployment, and my Report Server migration piece is crossed off!