`delete_files` command for `transform`

[srthkdb]

In Issue #416 (JSON output form scancode toolkit doesn't work as the input for gen), we would like to delete files items with low license score. To do this, a delete_files command for transform would be needed, as the current version of transform cannot remove items from a list. Should this feature be added because we might end up making aboutcode-toolkit more complicated than it was originally intended to be?

[chinyeungli]

I think this featuer makes aboutcode-tk more complicated than it originally intended to be, but this is open for discussion.

[chinyeungli]

I don't think this is needed. Closing it.