Sometimes emptying your recycling bin will speed up uninstall. We are working with adobe to improve the extension manager performance and also working on an alternative installation and uninstall experience to try to fix the problem ourselves.
Usually the uninstall will complete if you close Dreamweaver first and be patient. Of course deleting the configuration folder is always an option, and unfortunately is ofent quicker than uninstalling, since installing happens very quickly. I'm not really sure why the extension manager takes so long to uninstall but installs so quickly, but unfortunately it can make deleting the configuration folder the most efficient technique.
We aplogize for the inconvenience and assure you that we will put considerable effort into addressing the problem.