chore: Fix issues with notification actors (#1807)

db/migrate/20210219085719_remove_old_notifications.rb

@@ -0,0 +1,5 @@
+class RemoveOldNotifications < ActiveRecord::Migration[6.0]
+  def change
+    Notification.where(notification_type: 'assigned_conversation_new_message').destroy_all
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2021_02_17_154129) do
+ActiveRecord::Schema.define(version: 2021_02_19_085719) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_stat_statements"