how do I delete an Eclipse project when I've already deleted the folder and contents?

http://superuser.com/questions/253831/how-do-i-delete-an-eclipse-project-when-ive-already-deleted-the-folder-and-cont

Try removing directly the project within your workspace, within:

<workspace>\.metadata\.plugins\org.eclipse.core.resources\.projects\

as mentioned in "Where in an Eclipse workspace is the list of projects stored?"