Remove installation of ffi package
Remove installation of ffi package

We no longer need this explicitly defined in Puppet as we define the
version in the govuk_seed_crawler Gem:
https://github.com/alphagov/govuk_seed_crawler/pull/8/commits/0ee46d44c62eeeefbc37ddad3a49532dcf8f1c16

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet