remove some unused imports (#260)

* remove some unused imports

as suggested by lgtm

https://lgtm.com/projects/g/yaml/pyyaml/

* add back import * from nodes

* remove also sys import

* remove mkpath import

lib/yaml/representer.py

@@ -3,11 +3,12 @@
     'RepresenterError']
 
 from error import *
+
 from nodes import *
 
 import datetime
 
-import sys, copy_reg, types
+import copy_reg, types
 
 class RepresenterError(YAMLError):
     pass

lib3/yaml/representer.py

@@ -5,7 +5,7 @@
 from .error import *
 from .nodes import *
 
-import datetime, sys, copyreg, types, base64, collections
+import datetime, copyreg, types, base64, collections
 
 class RepresenterError(YAMLError):
     pass

setup.py

@@ -65,7 +65,6 @@
 from distutils.core import setup, Command
 from distutils.core import Distribution as _Distribution
 from distutils.core import Extension as _Extension
-from distutils.dir_util import mkpath
 from distutils.command.build_ext import build_ext as _build_ext
 from distutils.command.bdist_rpm import bdist_rpm as _bdist_rpm
 from distutils.errors import DistutilsError, CompileError, LinkError, DistutilsPlatformError