User, Webfinger: Remove OStatus vestiges

Mainly the `magic_key` field

priv/repo/migrations/20200505072231_remove_magic_key_field.exs

@@ -0,0 +1,9 @@
+defmodule Pleroma.Repo.Migrations.RemoveMagicKeyField do
+  use Ecto.Migration
+
+  def change do
+    alter table(:users) do
+      remove(:magic_key, :string)
+    end
+  end
+end