Remove unused imports

A few places still imported the compat module for no reason - this
commit fixes that.

polymorphic/query.py

@@ -9,7 +9,6 @@ from django.contrib.contenttypes.models import ContentType
 from django.core.exceptions import FieldDoesNotExist
 from django.db.models.query import ModelIterable, Q, QuerySet
 
-from . import compat
 from .query_translate import (
     translate_polymorphic_field_path,
     translate_polymorphic_filter_definitions_in_args,

polymorphic/showfields.py

@@ -3,8 +3,6 @@ import re
 
 from django.db import models
 
-from . import compat
-
 RE_DEFERRED = re.compile("_Deferred_.*")
 
 

polymorphic/templatetags/polymorphic_admin_tags.py

@@ -1,7 +1,5 @@
 from django.template import Library, Node, TemplateSyntaxError
 
-from polymorphic import compat
-
 register = Library()