title: Remove past migration in rails
body: <p>I created quite a lot of migrations since the beginning of my rails app. Some of them where just for test purposes. I now have a lot of migrations that are totally useless (eg: create a table in a migration and drop it in the next one).  </p>
  
  <p>As schema.rb get updated once db:migrate is ran, is it possible to delete all the migrations and to start from the actual content of schema.rb ?</p>