Remove the mojo serial interfaces and related infrastructure.

device/serial/serial_serialization.mojom

-// Copyright 2014 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-module device.serial;
-
-import "serial.mojom";
-import "data_stream_serialization.mojom";
-
-// The client state of a serial connection.
-struct ConnectionState {
-  uint32 connectionId;
-  bool paused = false;
-  bool persistent = false;
-  string name = "";
-  uint32 receiveTimeout = 0;
-  uint32 sendTimeout = 0;
-  uint32 bufferSize = 4096;
-};
-
-// A serialized serial connection.
-struct SerializedConnection {
-  ConnectionState state;
-  ReceiveError queuedReceiveError = NONE;
-  array<int8>? queuedReceiveData;
-  Connection connection;
-  SerializedDataSender sender;
-  SerializedDataReceiver receiver;
-};