Revert of [cast_channel] Move cast_channel related files from //extensions to //components

components/cast_channel/proto/BUILD.gn

Index: components/cast_channel/proto/BUILD.gn
diff --git a/components/cast_channel/proto/BUILD.gn b/components/cast_channel/proto/BUILD.gn
deleted file mode 100644
index e7d76b388dfdfdf044d24154d8f512cff860d5e3..0000000000000000000000000000000000000000
--- a/components/cast_channel/proto/BUILD.gn
+++ /dev/null
@@ -1,13 +0,0 @@
-# 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.
-
-import("//third_party/protobuf/proto_library.gni")
-
-proto_library("cast_channel_proto") {
-  sources = [
-    "authority_keys.proto",
-    "cast_channel.proto",
-    "logging.proto",
-  ]
-}