Remove duplicate dependencies
Remove duplicate dependencies

'del' and 'gulp' packages were listed in both dependencies
and devDependencies, producing a warning on npm install.
They are now only in devDependencies, so warning should be removed.

[hotfix]

ministryofjustice/manchester_traffic_offences_pleas,ministryofjustice/manchester_traffic_offences_pleas,ministryofjustice/manchester_traffic_offences_pleas,ministryofjustice/manchester_traffic_offences_pleas