[PENNYPALOOZA] Remove unused rst

[doctorperceptron]

We no longer use the demonstrations.rst file or the CircleCI config for this project. Sphinx still needs an index.rst file to build, but it can be (and now is) empty. Removing these clears up a lot of the warnings that Sphinx was previously throwing during builds.

Note: Also cleaned up a small config bug with Sphinx. Newer versions require you to set the language parameter.

Example of building the gbs demo with these changes:

Running Sphinx v5.3.0
Using pandoc version: 3.7.0.1 to convert rst text blocks to markdown for .ipynb files
loading pickled environment... done
generating gallery...
generating gallery for demos... [100%] gbs.py                                                                                                    
building [mo]: targets for 0 po files that are out of date
building [json]: targets for 3 source files that are out of date
updating environment: 0 added, 3 changed, 0 removed
reading sources... [100%] demos/sg_execution_times                                                                                               
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
writing output... [100%] index                                                                                                                   
generating indices... genindex done
writing additional pages... search done
copying images... [100%] demos/images/thumb/sphx_glr_gbs_thumb.png                                                                               
copying downloadable files... [100%] demos/demos_jupyter.zip                                                                                     
copying static files... done
copying extra files... done
dumping search index in English (code: en)... done
dumping object inventory... done
Sphinx-Gallery gallery_conf["plot_gallery"] was False, so no examples were executed.
build succeeded.

You can now process the JSON files in _build/json.

[Alan-eMartin]

https://media4.giphy.com/media/v1.Y2lkPTc5MGI3NjExbWJ3MTE2bWEycjZvMDlwNWd5dmw5Y2hjNHFlb3Z3MzRhOTBmajdhYiZlcD12MV9pbnRlcm5hbF9naWZfYnlfaWQmY3Q9Zw/gRDPR4Ox17FqixTmfS/giphy.gif

[Alan-eMartin]

🫤