[MNT]: Remove the userdemo section in examples

[timhoffm]

Summary

https://matplotlib.org/devdocs/gallery/index.html#userdemo

This section was a collection of plots used via .. literalinclude:: in the user documentation.

It's existence was only motivated structurally. This does not fit with the semantic sectioning of the examples. Userdemo should thus be removed.

Proposed fix

If the examples are still used in an .. literalinclude::, they should be converted to a figure directive.

If they are not used anymore, they should either

• be deleted if they do not contain relevant new aspects (e.g. [Doc]: Delete examples made redundant by annotation tutorial rewrite (annotate_simple01, ...) #24723) or
• be relocated to other sections.

[QuLogic]

If the examples are still used in an .. literallyinclude::, they should be converted to a figure directive.

I don't believe there are any cases of this markup.

[timhoffm]

Sorry, typo in the directive. It is .. literalinclude::

[enriched-h]

Hi @timhoffm I am new to open source and I would like to be assigned this issue. Can you please provide guidance on how I can resolve this issue.

[rcomer]

Hi @enriched-h you are welcome to submit a pull request for any issue, but we do not assign them. Feel free to ask any specific questions about this issue here or, if you prefer, in our incubator gitter room.

Please also see our contributors’ guide:
https://matplotlib.org/devdocs/devel/contributing.html