title: Remove ecto migration from the plan
body: <p>I generated a migration by</p>
  
  <pre><code>mix ecto.gen.migration migration_name
  </code></pre>
  
  <p>I did not run the migration and decided not to run it at all.
  I deleted the migration file from priv folder, however, it still appears in the migration plan. Is there any way how to delete such a migration?</p>