Fix event unsigned having default empty map in db

lib/architex/schema/event.ex

@@ -6,7 +6,6 @@ defmodule Architex.Event do
   alias Architex.{Repo, Room, Event, Account, EncodableMap, KeyServer}
   alias Architex.Types.UserId
 
-  # TODO: It seems unsigned is always set in DB, even though it is not specified?
   @type t :: %__MODULE__{
           nid: integer(),
           id: String.t(),

priv/repo/migrations/20210830160818_create_initial_tables.exs

@@ -43,7 +43,7 @@ defmodule Architex.Repo.Migrations.CreateInitialTables do
       add :signatures, :map, null: false
       add :state_key, :string, null: true
       add :type, :string, null: false
-      add :unsigned, :map, default: %{}, null: true
+      add :unsigned, :map, null: true
     end
 
     create index(:events, [:id], unique: true)