Chats: Remove unread from the db, calculate from unseen messages.

priv/repo/migrations/20200603120448_remove_unread_from_chats.exs

@@ -0,0 +1,9 @@
+defmodule Pleroma.Repo.Migrations.RemoveUnreadFromChats do
+  use Ecto.Migration
+
+  def change do
+    alter table(:chats) do
+      remove(:unread, :integer, default: 0)
+    end
+  end
+end