removeById method
Tombstones the element with id (no-op if unknown).
Implementation
RgaList<T> removeById(String id) {
final node = _nodes[id];
if (node == null || node.deleted) return this;
final nodes = Map<String, RgaNode<T>>.from(_nodes);
nodes[id] = node.tombstone();
return RgaList._(replicaId, nodes, _counter);
}