title: Best way to remove column from CSC Matrix
body: <p>Lest say I have the following Sparse Matrix:</p>
  <pre><code>A = sparse([1 4 7; 2 5 8; 3 6 9])
  </code></pre>
  <p>What is the most efficient way to get:</p>
  <pre><code>A = sparse([1 0 7; 2 0 8; 3 0 9])
  </code></pre>
  <p>The actual matrix I'm using is actually a lot bigger...</p>