Remove remaining unused imports in webkitpy.

third_party/WebKit/Tools/Scripts/webkitpy/common/system/executive.py

 # Copyright (c) 2009, Google Inc. All rights reserved.
 # Copyright (c) 2009 Apple Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 17 matching lines @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 import csv
 import errno
 import logging
 import multiprocessing
 import os
 import signal
 import subprocess
 import sys
+import threading
 import time
-import threading
 
 from webkitpy.common.system.filesystem import FileSystem
 
 
 _log = logging.getLogger(__name__)
 
 
 class ScriptError(Exception):
 
     def __init__(self,
@@ skipping 418 matching lines @@
             pool.close()
             pool.join()
 
 
 def _run_command_thunk(cmd_line_and_cwd):
     # Note that this needs to be a bare module (and hence Picklable) method to work with multiprocessing.Pool.
     (cmd_line, cwd) = cmd_line_and_cwd
     proc = subprocess.Popen(cmd_line, cwd=cwd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
     stdout, stderr = proc.communicate()
     return (proc.returncode, stdout, stderr)