title: Use Rails Migrations to delete an index without knowing its name
body: <p>I have a table with a compound index that wasn't created through a rails migration. Now, I need to create a rails migration that will delete this index and create a new one, but I don't necessarily know what the name of the index will be.</p>
  
  <p>I know that it is possible to get a list of table names and column names within a migration step. Is it possible to get a list of index names on a particular table? Or, looking at it another way, is it possible to delete <em>all</em> indexes on a table? Or is the only option to write my own database-specific SQL queries to get this info?</p>