Remove unnecessary "mac" meta data tag from Android Manifest

chrome/android/webapk/shell_apk/BUILD.gn

 # 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.
 
 import("//build/config/android/rules.gni")
 
 declare_args() {
   # The origin URL of the WebAPK. Used to generate a unique package name for
   # WebAPK. Example: "foo.com"
   webapk_manifest_package_origin = "template"
 
   # The URL that the WebAPK should navigate to when it is launched.
   webapk_start_url = "https://www.template.com/home_page"
 
   # The browser that the WebAPK will be bound to.
   webapk_runtime_host = "com.google.android.apps.chrome"
 
-  # The message authentication code from Chrome for identity verification.
-  webapk_mac = "template"
-
   # The scope of the urls that the WebAPK can navigate to.
   webapk_scope_url = "https://www.template.com"
 
   # Host part of |webapk_scope|.
   webapk_scope_url_host = "www.template.com"
 }
 
 shell_apk_manifest_package =
     "org.chromium.webapk.$webapk_manifest_package_origin"
 
 shell_apk_manifest = "$target_gen_dir/shell_apk_manifest/AndroidManifest.xml"
 
 jinja_template("shell_apk_manifest") {
   input = "AndroidManifest.xml"
   output = shell_apk_manifest
 
   variables = [
     "manifest_package=$shell_apk_manifest_package",
     "host_url=$webapk_start_url",
     "runtime_host=$webapk_runtime_host",
-    "mac=$webapk_mac",
     "scope_url=$webapk_scope_url",
     "scope_url_host=$webapk_scope_url_host",
   ]
 }
 
 android_resources("shell_apk_resources") {
   resource_dirs = [ "res" ]
   custom_package = "org.chromium.webapk.shell_apk"
 }
 
@@ skipping 26 matching lines @@
       [ "javatests/src/org/chromium/webapk/shell_apk/DexLoaderTest.java" ]
   deps = [
     ":dex_loader_lib",
     "//base:base_java",
     "//base:base_java_test_support",
     "//chrome/android/webapk/libs/common",
     "//content/public/test/android:content_java_test_support",
   ]
   srcjar_deps = [ "javatests/dex_optimizer:dex_optimizer_service_aidl" ]
 }