Remove one attachment from a transaction entry. Only this entry is affected. Returns 404 if the entry does not exist or is not accessible to the current operator, or if the attachment is not attached to this entry. The image file itself is not deleted from storage: its URL may keep working after the attachment is removed, so do not rely on deletion to make a shared link private. Deleting an attachment does not change the entry's updated_at and does not send a webhook. Requires a token with write access.