android envsetup: Stop exporting ANDROID_NDK_ROOT.

build/android/pylib/utils/emulator.py

 # Copyright (c) 2012 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.
 
 """Provides an interface to start and stop Android emulator.
 
-Assumes system environment ANDROID_NDK_ROOT has been set.
-
   Emulator: The class provides the methods to launch/shutdown the emulator with
             the android virtual device named 'avd_armeabi' .
 """
 
 import logging
 import os
 import signal
 import subprocess
 import time
 
@@ skipping 414 matching lines @@
     logging.critical('emulator _ShutdownOnSignal')
     for sig in self._SIGNALS:
       signal.signal(sig, signal.SIG_DFL)
     self.Shutdown()
     raise KeyboardInterrupt  # print a stack
 
   def _InstallKillHandler(self):
     """Install a handler to kill the emulator when we exit unexpectedly."""
     for sig in self._SIGNALS:
       signal.signal(sig, self._ShutdownOnSignal)