Don't use nbsphinx_prompt_width to hide prompts

[mgeier]

I'm creating this issue because your repo contains a conf.py file with

nbsphinx_prompt_width = 0

... presumably in an attempt to remove the prompts from code cells.

I just want to give you a heads-up that this will stop working once https://github.com/spatialaudio/nbsphinx/pull/439 is merged.

For more reliable alternatives, see https://nbsphinx.readthedocs.io/en/latest/custom-css.html.