Move memory_coordinator_client and its registry to base/memory

components/memory_coordinator/common/BUILD.gn

 # Copyright 2016 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.
 
 component("common") {
   output_name = "memory_coordinator_common"
 
   sources = [
-    "client_registry.cc",
-    "client_registry.h",
-    "memory_coordinator_client.h",
     "memory_coordinator_export.h",
     "memory_coordinator_features.cc",
     "memory_coordinator_features.h",
   ]
 
   defines = [ "MEMORY_COORDINATOR_IMPLEMENTATION" ]
 
   deps = [
     "//base",
   ]
 
   public_deps = [
     "//components/memory_coordinator/public/interfaces",
   ]
 }