remove and element from array firebase swift 5
let washingtonRef = db.collection("cities").document("DC")
// Atomically add a new region to the "regions" array field.
washingtonRef.updateData([
"regions": FieldValue.arrayUnion(["greater_virginia"])
])
// Atomically remove a region from the "regions" array field.
washingtonRef.updateData([
"regions": FieldValue.arrayRemove(["east_coast"])
])