Fix flake8 errors

src/olympia/api/permissions.py

@@ -1,7 +1,6 @@
 from rest_framework.exceptions import MethodNotAllowed
 from rest_framework.permissions import SAFE_METHODS, BasePermission
 
-from olympia import amo
 from olympia.amo import permissions
 from olympia.access import acl
 

src/olympia/reviewers/models.py

@@ -7,7 +7,7 @@ from django.conf import settings
 from django.core.cache import cache
 from django.db import models
 from django.db.models import Q, Sum
-from django.db.models.functions import Coalesce, Func
+from django.db.models.functions import Func
 from django.template import loader
 from django.utils.translation import ugettext, ugettext_lazy as _
 

src/olympia/reviewers/tests/test_views.py

@@ -39,7 +39,7 @@ from olympia.reviewers.models import (
     AutoApprovalSummary, RereviewQueueTheme, ReviewerScore,
     ReviewerSubscription, Whiteboard)
 from olympia.users.models import UserProfile
-from olympia.versions.models import ApplicationsVersions, AppVersion, Version
+from olympia.versions.models import ApplicationsVersions, AppVersion
 from olympia.zadmin.models import get_config, set_config