Invalid songs / files still in the library

Steps to reproduce

1. Import an album / tracks via the command line using the --in-place flag.
2. Delete the files from disk
3. Run manage check_inplace_files --no-dry-run - this will list the files as removed (which is intended)
4. Run manage prune_library --tracks --albums --artists --no-dry-run

What happens?

The artist / album still show up in the library with N/A for all fields and the tracks are unplayable.

What is expected?

This should be removed completely from the library.

Context

Funkwhale version(s) affected: x.y

Version 0.20.1