Remove the unmaintained performance monitor.

chrome/browser/performance_monitor/BUILD.gn

Index: chrome/browser/performance_monitor/BUILD.gn
diff --git a/chrome/browser/performance_monitor/BUILD.gn b/chrome/browser/performance_monitor/BUILD.gn
deleted file mode 100644
index a763a6c78b7c44c7121b24f3d47ede8cfca28b62..0000000000000000000000000000000000000000
--- a/chrome/browser/performance_monitor/BUILD.gn
+++ /dev/null
@@ -1,11 +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("//extensions/generated_extensions_api.gni")
-
-generated_extensions_api("performance_monitor") {
-  sources = [ "events.json" ]
-  root_namespace = "performance_monitor::%(namespace)s"
-  schemas = true
-}