Offer to remove module dependencies that are no longer needed

Description of the need On Linux, when you remove a package that has dependencies (which aren't used by any other installed package), you'll be told that those dependencies are no longer needed and can be safely removed. It'd be cool to have something similar in Backdrop. This would help to reduce situations where a site has modules installed that it doesn't need because the module(s) that depended on them was uninstalled (e.g. Libraries, Field Formatter Settings, etc.).

Proposed solution No idea, just putting the thought out there :smiley: