Add a migration to clean up activity_expirations table

priv/repo/migrations/20200804180322_remove_nonlocal_expirations.exs

@@ -0,0 +1,19 @@
+defmodule Pleroma.Repo.Migrations.RemoveNonlocalExpirations do
+  use Ecto.Migration
+
+  def up do
+    statement = """
+    DELETE FROM
+      activity_expirations A USING activities B
+    WHERE
+      A.activity_id = B.id
+      AND B.local = false;
+    """
+
+    execute(statement)
+  end
+
+  def down do
+    :ok
+  end
+end