various unused imports removed (I am allergic)

mongoengine/base/datastructures.py

@@ -1,5 +1,4 @@
 import weakref
-import functools
 import itertools
 from mongoengine.common import _import_class
 from mongoengine.errors import DoesNotExist, MultipleObjectsReturned

mongoengine/base/metaclasses.py

@@ -1,13 +1,11 @@
 import warnings
 
-import pymongo
-
 from mongoengine.common import _import_class
 from mongoengine.errors import InvalidDocumentError
 from mongoengine.python_support import PY3
 from mongoengine.queryset import (DO_NOTHING, DoesNotExist,
                                   MultipleObjectsReturned,
-                                  QuerySet, QuerySetManager)
+                                  QuerySetManager)
 
 from mongoengine.base.common import _document_registry, ALLOW_INHERITANCE
 from mongoengine.base.fields import BaseField, ComplexBaseField, ObjectIdField