title: how to drop duplicated columns data based on column name in pandas
body: <p>Assume I have a table like below</p>
  <pre><code>    A   B   C   B
  0   0   1   2   3
  1   4   5   6   7
  </code></pre>
  <p>I'd like to drop column B. I tried to use <code>drop_duplicates</code>, but it seems that it only works based on duplicated data not header.
  Hope anyone know how to do this.</p>