title: Delete second row of header in PANDAS
body: <p>I have a dataframe in PANDAS which has two lines of headers.How could I remove the second line? For example, I have the following:</p>
  
  <pre><code>         AA  BB  CC  DD
           A   B   C   D
  Index    
     1     1   2   3   4
     2     5   6   7   8
     3     9   1   2   3
  </code></pre>
  
  <p>and I would like to get something like this:</p>
  
  <pre><code>         AA  BB  CC  DD
  Index    
     1     1   2   3   4
     2     5   6   7   8
     3     9   1   2   3
  </code></pre>
  
  <p>Thank you very much.</p>