chor(remove unnecessary map)

Author: BenjaminHorn

lib/utilities/relationship-utils.js

@@ -157,14 +157,13 @@ function updateHasManyThrough (
   return PivotModel.find({ where: { [leftFKName]: leftPKValue } })
     .then(models => {
       const existingIds = models.map(model => model[rightFKName])
-      const newIds = rightFKValues.map(id => id)
-      const idsToDelete = _.difference(existingIds, newIds)
+      const idsToDelete = _.difference(existingIds, rightFKValues)
       return PivotModel.destroyAll({
         [leftFKName]: leftPKValue,
         [rightFKName]: { inq: idsToDelete }
       })
         .then(() => {
-          const idsToAdd = _.difference(newIds, existingIds)
+          const idsToAdd = _.difference(rightFKValues, existingIds)
           return PivotModel.create(
             idsToAdd.map(id => ({
               [leftFKName]: leftPKValue,