Remove the use of schedule_for in post_notifications.

Years ago we started to implement a way to schedule a notification. We hit a problem but we never came up with a good solution and the feature never made it back to the top of the priority list.

This PR removes the code for scheduled_for. There will be another PR to drop the scheduled_notifications table and remove the schedule_notifications service permission

Unfortunately, I don't think we can remove the `scheduled_for` attribute from the notification.serialized method because out clients might fail if something is missing. For now I have left it in but defaulted the value to None.

app/notifications/validators.py

@@ -12,7 +12,7 @@ from app.dao import services_dao
 from app.dao.service_sms_sender_dao import dao_get_service_sms_senders_by_id
 from app.models import (
     INTERNATIONAL_SMS_TYPE, SMS_TYPE, EMAIL_TYPE, LETTER_TYPE,
-    KEY_TYPE_TEST, KEY_TYPE_TEAM, SCHEDULE_NOTIFICATIONS
+    KEY_TYPE_TEST, KEY_TYPE_TEAM
 )
 from app.service.utils import service_allowed_to_send_to
 from app.v2.errors import TooManyRequestsError, BadRequestError, RateLimitError
@@ -108,12 +108,6 @@ def check_if_service_can_send_files_by_email(service_contact_link, service_id):
         )
 
 
-def check_service_can_schedule_notification(permissions, scheduled_for):
-    if scheduled_for:
-        if not service_has_permission(SCHEDULE_NOTIFICATIONS, permissions):
-            raise BadRequestError(message="Cannot schedule notifications (this feature is invite-only)")
-
-
 def validate_and_format_recipient(send_to, key_type, service, notification_type, allow_whitelisted_recipients=True):
     if send_to is None:
         raise BadRequestError(message="Recipient can't be empty")