Administration of Active Directory does not have to be hard. Too often what should be a simple task is made more difficult than it needs to be.The solution? Hyena from SystemTools Software. With ease-of-use as well as powerful importing and bulk updating capabilities.
You can uninstall the Exchange using ADSIEIDT, but it quite dangerous.
Have shutdown the Exchange 2007 server and everything is working as expected?
Below link is how to remove Exchange 2007 using ADSIEDIT.
https://social.technet.microsoft.com/Forums/exchange/en-US/84f21467-adaf-47f2-a2de-ca07017df784/removing-exchange-2007-that-no-longer-exists