Disable validations when saving after non-Maslow need_id strip

Since removing non-Maslow need_ids can touch archived artefacts as well,
the migration fails if validations are run upon saving.
`save!` and `validate: false` look odd together. it reads as: "raise exception `Mongoid::Errors::Validations` for validation errors, but don't run validations" :smile: computationally, this works. just noticed a cosmetic flaw, so pointed out.