Make challenge solution comments more consistent, remove numbering

[chrisdavidmills]

Description

As discussed with @hamishwillee, I wanted to update the comments in the Learn area challenge solutions to:

• Be more consistent
• Use the same or similar wording to the project brief headings and tasks so that it is more intuitive which solution relates to which challenge
• Remove the numbers, as most of the time they are a red herring and are not related to any numbered steps in the challenges.

This PR aims to fix these issues for the current challenges I've recently updated.

Motivation

Additional details

Related issues and pull requests

[github-actions]

Preview URLs (8 pages)

• /en-US/docs/Learn_web_development/Core/CSS_layout/Fundamental_Layout_Comprehension
• /en-US/docs/Learn_web_development/Core/CSS_layout/Mobile-first_challenge
• /en-US/docs/Learn_web_development/Core/Scripting/House_data_UI
• /en-US/docs/Learn_web_development/Core/Scripting/Image_gallery
• /en-US/docs/Learn_web_development/Core/Scripting/Silly_story_generator
• /en-US/docs/Learn_web_development/Core/Styling_basics/Fixing_blog_styles
• /en-US/docs/Learn_web_development/Core/Styling_basics/Size_decorate_content_panel
• /en-US/docs/Learn_web_development/Core/Text_styling/Typesetting_a_homepage

[hamishwillee]

Much better way of doing things. Thank you.