issue39 add stat tonpu hanchan for four

Author: enOnesohC

server/player/tenhou/models.py

@@ -4,7 +4,6 @@
 
 from django.db import models
 from django.db.models import F
-from django.db.models import Avg, Count, Case, When, FloatField
 from django.utils.translation import gettext_lazy
 
 from mahjong_portal.models import BaseModel