Removing aura_android.gni

aura_android.gni no longer needed as Android Aura project has been cancelled.

BUG=NONE

Review URL: https://codereview.chromium.org/1636143002

Cr-Commit-Position: refs/heads/master@{#371885}

build/args/aura_android.gni

-# 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.
-
-# This file contains the common overrides for building Aura on Android.
-# To enable Aura on Android, import this file from your gn args:
-#
-#    import("//build/args/aura_android.gni")
-
-target_os = "android"
-
-# features.gni overrides
-enable_extensions = true
-enable_plugins = true
-
-# ui.gni overrides
-use_aura = true
-android_java_ui = false
-toolkit_views = true