title: Unable to push to heroku after removing submodule
body: <p>I removed a submodule from my code, when I try to push to heroku now, I get:</p>
  
  <pre><code>remote: Git submodules detected, installing:
  remote: No submodule mapping found in .gitmodules for path 'submodule/path'
  remote:
  remote: ! Push rejected, submodule install failed
  remote:
  </code></pre>
  
  <p>I am using Heroku's buildpack: <a href="https://github.com/heroku/heroku-buildpack-multi.git" rel="noreferrer">https://github.com/heroku/heroku-buildpack-multi.git</a></p>
  
  <p>With this <code>.buildpacks</code> file:</p>
  
  <pre><code>https://github.com/ello/heroku-buildpack-imagemagick-cedar-14
  https://github.com/heroku/heroku-buildpack-ruby.git
  </code></pre>
  
  <p>Is there something I can do to fix this? Do I just need to delete this app and start a new one (this is obviously very undesirable).</p>