Mobile Publisher: Cannot Delete Mobile Publisher Application Projects

In the current behavior, Mobile Publisher application projects that have been created cannot be deleted.
Existing Mobile Publisher application projects can be confirmed from [Setup] > [Mobile Publisher].

This behavior is by design; however, you can vote for this as a future feature request on IdeaExchange (Remove Deprecated Mobile Publisher Apps).By visiting the page above and clicking the [Upvote] icon, you can show your support and points will be added to that post.
While this feature has not yet been implemented, we strive to reflect customer-submitted "requests," "new feature ideas," and "ideas you'd like to see realized" in future product releases as much as possible — we encourage you to take advantage of this opportunity.

Ref: IdeaExchange Status Definitions