title: Git: Delete one of two parent commits
body: <p>I have the following commit history:</p>
  
  <pre><code>  A--B--C branch1
   /     /
  I      D
   \
    \
     J branch2
  </code></pre>
  
  <p>and I want to simply delete commit D, which isn't connected elsewhere.</p>
  
  <p>I tried <code>git rebase --onto B C</code>, but for some reason this deletes C as well and produces</p>
  
  <pre><code>  A--B branch1
   /     
  I      
   \
    \
     J branch2
  </code></pre>