Delete Web/Demos page

[hamishwillee]

This deletes the Web demos page, which contains a list of user-contributed demo software.

The main reasons are:

• The page is not really appropriate for a docs site.
• There are no criteria for addition and removal - it is essentially unmaintained
• The links don't really fit with the writing guidelines
• This was only linked in one place - so in no way essential.

The demos themselves are somewhat interesting, but not necessarily easy to digest.

FYI @estelle @wbamberg

[github-actions]

Preview URLs

• /en-US/docs/Web/CSS

External URLs (11)

URL: /en-US/docs/Web/CSS
Title: CSS: Cascading Style Sheets

• https://addons.mozilla.org/en-US/firefox/addon/web-developer/ (1 time)
• https://bugzil.la/1323667 (1 time)
• https://drafts.csswg.org/css-color-5/ (1 time)
• https://firefox-source-docs.mozilla.org/devtools-user/index.html (1 time)
• https://firefox-source-docs.mozilla.org/devtools-user/page_inspector/index.html (1 time)
• https://firefox-source-docs.mozilla.org/devtools-user/style_editor/index.html (1 time)
• https://jigsaw.w3.org/css-validator/ (1 time)
• https://stackoverflow.com/questions/tagged/css (1 time)
• https://www.w3.org/Style/CSS/ (1 time)
• https://www.w3.org/Style/CSS/current-work (1 time)
• https://www.w3.org/TR/css/ (1 time)