improve learning area landing page

[chrisdavidmills]

Description

As part of launching the MDN curriculum, we are making some changes to the main MDN content, as discussed in https://github.com/orgs/mdn/discussions/633 (see the "Changes we intend to make" heading).

This PR implements points 2, 4, and 5 from that list — making the language work slightly better alongside the MDN Curriculum (although TBH, #32513 does quite a bit of this work), improving the "Tasks and assessments" section so that it just makes a bit more sense, and trimming down the list of "See also" links.

For the see also links, I'd like to note the following:

1. I moved the blog and newsletter links down the bottom of the list, as I felt they were less useful to the target audience than the immediate learning resources
2. I Removed the (Web demystified)[https://www.youtube.com/playlist?list=PLo3w8EB99pqLEopnunz-dOOBJ8t-Wgt2g] link, as it is 6 years old, and not going to be updated any time soon.
3. I removed the https://www.bitdegree.org/learn/ link as it seems rather out of date, and very ad-heavy
4. I removed the https://foundation.mozilla.org/en/initiatives/web-literacy/core-curriculum/ link. The link doesn’t seem to go where you’d expect, and when you get there, many of the linked resources 404. Out of date.
5. I removed the code.org link as it is not immediately obvious where to get started.
6. I removed the edabit link as it was last updated in 2021.

Motivation

Additional details

Related issues and pull requests

[github-actions]

Preview URLs

• /en-US/docs/Learn

External URLs (1)

URL: /en-US/docs/Learn
Title: Learn web development

• https://www.mozilla.org/en-US/newsletter/developer/ (1 time) (Note! This may be a new URL 👀)