[3.6] Remove unused imports (#2104)

Part of patch by Serhiy Strochaka, 2016-12-16 (no bpo issue)
(cherry-pick of 70d28a184c)

Lib/idlelib/idle_test/test_macosx.py

@@ -4,7 +4,6 @@ Coverage: 71% on Windows.
 '''
 from idlelib import macosx
 from test.support import requires
-import sys
 import tkinter as tk
 import unittest
 import unittest.mock as mock

Lib/idlelib/idle_test/test_tree.py

@@ -5,7 +5,6 @@ Coverage: 56%
 from idlelib import tree
 from test.support import requires
 requires('gui')
-import os
 import unittest
 from tkinter import Tk
 

Lib/idlelib/macosx.py

@@ -2,7 +2,6 @@
 A number of functions that enhance IDLE on Mac OSX.
 """
 from sys import platform  # Used in _init_tk_type, changed by test.
-import warnings
 
 import tkinter
 

Lib/idlelib/stackviewer.py

@@ -1,6 +1,5 @@
 import linecache
 import os
-import re
 import sys
 
 import tkinter as tk