Remove unused imports.

rest_framework/decorators.py

@@ -10,7 +10,6 @@ from __future__ import unicode_literals
 from django.utils import six
 from rest_framework.views import APIView
 import types
-import warnings
 
 
 def api_view(http_method_names):

rest_framework/generics.py

@@ -11,7 +11,6 @@ from django.utils.translation import ugettext as _
 from rest_framework import views, mixins, exceptions
 from rest_framework.request import clone_request
 from rest_framework.settings import api_settings
-import warnings
 
 
 def strict_positive_int(integer_string, cutoff=None):