Remove hard reference to GFM since IPythonGFM uses CM require to load it.

IPython/html/templates/notebook.html

@@ -313,7 +313,6 @@ class="notebook_app"
 <script src="{{ static_url("components/codemirror/mode/css/css.js") }}" charset="utf-8"></script>
 <script src="{{ static_url("components/codemirror/mode/rst/rst.js") }}" charset="utf-8"></script>
 <script src="{{ static_url("components/codemirror/mode/markdown/markdown.js") }}" charset="utf-8"></script>
-<script src="{{ static_url("components/codemirror/mode/gfm/gfm.js") }}" charset="utf-8"></script>
 <script src="{{ static_url("components/codemirror/mode/python/python.js") }}" charset="utf-8"></script>
 <script src="{{ static_url("notebook/js/codemirror-ipython.js") }}" charset="utf-8"></script>
 <script src="{{ static_url("notebook/js/codemirror-ipythongfm.js") }}" charset="utf-8"></script>