title: drop multiindex level but keep names of columns - pandas
body: <p>I have a <code>df</code> that looks like this</p>
  
  <pre><code>   a     b      c
                c1  c2
  0  87    33   32  34
  1  32    10   45  62
  2  78    83   99  71
  </code></pre>
  
  <p>I'd like to drop the <code>c</code> level but keep all the other column names</p>
  
  <pre><code>   a     b    c1  c2
  0  87    33   32  34
  1  32    10   45  62
  2  78    83   99  71
  </code></pre>
  
  <p><code>df.columns = df.columns.droplevel(0)</code> works but the names of <code>a</code> and <code>b</code> disappear</p>
  
  <pre><code>              c1  c2
  0  87    33   32  34
  1  32    10   45  62
  2  78    83   99  71
  </code></pre>