bpo-29919: Remove unused imports found by pyflakes (#137)

Make also minor PEP8 coding style fixes on modified imports.
diff --git a/Lib/lib2to3/pgen2/grammar.py b/Lib/lib2to3/pgen2/grammar.py
index 321e25e..c10dcfa 100644
--- a/Lib/lib2to3/pgen2/grammar.py
+++ b/Lib/lib2to3/pgen2/grammar.py
@@ -17,7 +17,7 @@
 import pickle
 
 # Local imports
-from . import token, tokenize
+from . import token
 
 
 class Grammar(object):