Completely remove Web/Guide and Web/Tutorials

[Josh-Cena]

Removed two subareas.

• Challenge solutions is undiscoverable from practically anywhere, so just removed it without redirect.
• "CSS layout" is moved to the CSS subtree. @estelle might want to find a better home for it.
• The "Guide" landing page seems to include a lot of different Web/ subareas, so redirecting it to Web/ instead of Learn/ seems more appropriate.

[github-actions]

Preview URLs

• /en-US/docs/Web/Accessibility
• /en-US/docs/Web/CSS/CSS_Layout
• /en-US/docs/Web/SVG/Tutorial/SVG_and_CSS
• /en-US/docs/Web

External URLs (8)

URL: /en-US/docs/Web
Title: Web technology for developers

• https://developer.chrome.com/docs/devtools/ (1 time)
• https://docs.microsoft.com/microsoft-edge/devtools-guide-chromium/landing/ (1 time)
• https://firefox-source-docs.mozilla.org/devtools-user/index.html (1 time)
• https://webkit.org/web-inspector/ (1 time)

---

URL: /en-US/docs/Web/Accessibility
Title: Accessibility

• https://www.w3.org/WAI/about/groups/waiig/ (1 time)
• https://www.w3.org/standards/webdesign/accessibility (1 time)

---

URL: /en-US/docs/Web/SVG/Tutorial/SVG_and_CSS
Title: SVG and CSS

• Need to better define what rules apply to an element in an <svg:use> subtree. w3c/svgwg#504 (1 time)
• https://www.w3.org/TR/SVG2/struct.html (1 time)

[dipikabh]

Hi @Josh-Cena, I am temporarily reverting this PR until we've assessed the SEO impact of these changes.