Remove unused imports throughout project

Unused imports were discovered using flake8. By removing the unused
imports, the code is a bit friendlier to new contributors as it is
clearer what is being used and not simply leftover from previous
refactoring.

The flake8 command:

$ flake8 . --select F401

http://flake8.pycqa.org/

1 files changed, 1 insertions, 1 deletions

diff --git a/pyparsing.py b/pyparsing.py
index 44773be..aa1b993 100644
--- a/pyparsing.py
+++ b/pyparsing.py
@@ -109,7 +109,7 @@ import pprint
 import traceback
 import types
 from datetime import datetime
-from itertools import takewhile
+
 try:
     # Python 3
     from itertools import filterfalse