If you want to completely wipe all traces of Exchange Server 2013 from your Active Directory then follow this simple instructions. This has worked thus far for me but perhaps I missed something so feel free to provide any feedback you may have.
Removing Exchange from AD is not something you might want to do carelessly. It should be obvious that wiping this information should be equivalent to starting your whole Exchange Infrastructure from scratch. This may result on losing mailboxes, emails, settings, email deliverability, etc. If you are familiar with the risks and understand what you are doing that’s fine, but if any of this sounds new to you then you should be most careful and seek professional help.
We are going to use the ADSIEdit tool which is used to edit Active Directory Metadata/Schema/etc. This is probably more delicate that messing with the Windows Registry so please proceed with extreme caution.
If you have access to your Exchange server you can delete a few things to leave it almost in pre-Exchange state. I strongly suggest you simply start from a fresh Windows Installation as it is hard to truly leave a server in a pre-exchange state.
Launch the IIS-Manager and delete the front and back end web sites.