title: Django DB index is present or not
body: <p>Suppose I have a model and <code>db_index=True</code>, so 1 migration file is created. Due to some reason I have Deleted the index directly in DB with PgAdmin. And also removed the <code>db_index=True</code> from model. Again it will try to apply migration with</p>
  <pre><code>  operations = [
              migrations.RemoveIndex(
                  model_name='Person',
                  name='name_idx',
              ),
  </code></pre>
  <p>So if i run this on my machine(where i have deleted the index) will raise error <code>ValueError(&quot;No index named %s on model %s&quot; % (name, self.name))</code>. Is there any way that I can do Delete index only if it is present.</p>