remove post_class and letterrate model

tests/app/db.py

@@ -45,7 +45,6 @@ from app.models import (
     InvitedOrganisationUser,
     InvitedUser,
     Job,
-    LetterRate,
     Notification,
     NotificationHistory,
     Organisation,
@@ -506,23 +505,6 @@ def create_rate(start_date, value, notification_type):
     return rate
 
 
-def create_letter_rate(start_date=None, end_date=None, crown=True, sheet_count=1, rate=0.33, post_class='second'):
-    if start_date is None:
-        start_date = datetime(2016, 1, 1)
-    rate = LetterRate(
-        id=uuid.uuid4(),
-        start_date=start_date,
-        end_date=end_date,
-        crown=crown,
-        sheet_count=sheet_count,
-        rate=rate,
-        post_class=post_class
-    )
-    db.session.add(rate)
-    db.session.commit()
-    return rate
-
-
 def create_api_key(service, key_type=KEY_TYPE_NORMAL, key_name=None):
     id_ = uuid.uuid4()