Pin nbsphinx to 0.8.6, clean up orphaned resources

CONTRIBUTING.rst

@@ -67,10 +67,6 @@ Verification
 While running the notebook, select one of your notebook files (the file will have the extension ``.ipynb``).
 In the top tab you will click on "Help" and then click on "About". In the pop window you will see information about the version of Jupyter that you are running. You will see "The version of the notebook server is:".
 If you are working in development mode, you will see that your version of Jupyter notebook will include the word "dev".
-
-.. image:: ./docs/source/_static/images/jupyter-verification.png
-   :width: 40pt
-
 If it does not include the word "dev", you are currently not working in development mode and should follow the steps below to uninstall and reinstall Jupyter.
 
 Troubleshooting the Installation

docs/doc-requirements.txt

@@ -1,5 +1,5 @@
 sphinx>=1.3.6
 sphinx-rtd-theme
-nbsphinx
+nbsphinx==0.8.6
 sphinxcontrib_github_alt
 myst_parser

docs/environment.yml

@@ -14,7 +14,7 @@ dependencies:
 - terminado
 - myst-parser
 - pip:
-  - nbsphinx
+  - nbsphinx==0.8.6
   - Send2Trash
   - prometheus_client
   - sphinxcontrib_github_alt

docs/source/examples/Notebook/header.md

@@ -1,4 +0,0 @@
-# Notebook Examples
-
-The pages in this section are all converted notebook files. You can also
-[view these notebooks on nbviewer](http://nbviewer.jupyter.org/github/jupyter/notebook/tree/master/)