I saw it before. Deletion Driven Development is one of the many names. For me a good rule of thumb is: removal of a feature should result in a diff that deletes a bunch of files (classes in case of oop) completely, and only single lines in other files: the call sites to that feature.
Are you saying "I can easily delete this code from the project" is a metric for modularity? That's really interesting, is it your own thought?