Revert of Enable RL by default

components/reading_list/core/BUILD.gn

Index: components/reading_list/core/BUILD.gn
diff --git a/components/reading_list/core/BUILD.gn b/components/reading_list/core/BUILD.gn
index f45b10c0b421a0dfb83bfe035648d24655d0c021..52dbc37326d1c354765936715725ca02e3978b5f 100644
--- a/components/reading_list/core/BUILD.gn
+++ b/components/reading_list/core/BUILD.gn
@@ -1,9 +1,6 @@
 # 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.
-
-import("//build/buildflag_header.gni")
-import("//components/reading_list/core/reading_list.gni")
 
 source_set("core") {
   sources = [
@@ -11,13 +8,6 @@
     "reading_list_switches.h",
   ]
   deps = [
-    ":reading_list_enable_flags",
     "//base",
   ]
 }
-
-buildflag_header("reading_list_enable_flags") {
-  header = "reading_list_enable_flags.h"
-  _enabled = is_ios && enable_reading_list
-  flags = [ "ENABLE_READING_LIST=$_enabled" ]
-}