Revert of Use element id's for animations

cc/proto/element_id.proto

Index: cc/proto/element_id.proto
diff --git a/cc/proto/element_id.proto b/cc/proto/element_id.proto
deleted file mode 100644
index 9e5cedd80a545e57009717cc25ebf0acc1bcb2c2..0000000000000000000000000000000000000000
--- a/cc/proto/element_id.proto
+++ /dev/null
@@ -1,18 +0,0 @@
-// Copyright 2015 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.
-
-syntax = "proto2";
-
-option optimize_for = LITE_RUNTIME;
-
-package cc.proto;
-
-// The message declared in this file corresponds to the class declared in
-// cc/animation/element_id.h
-
-// NEXT ID: 3
-message ElementId {
-  required int64 primary_id = 1;
-  required int64 secondary_id = 2;
-}