remove {{LearnBox}} macro and fix typo

[yin1999]

As a part of mdn/mdn-community#65.

chages:

• Update links by:

  1. removing https://developer.mozilla.org prefix.
  2. replacing /zh-TW/Learn with /zh-TW/docs/Learn

• remove empty HTML tags

[github-actions]

Preview URLs

• https://pr5480.content.dev.mdn.mozit.cloud/zh-TW/docs/Learn

Flaws

URL: /zh-TW/docs/Learn
Title: 學習該如何開發 Web
on GitHub
Flaw count: 44

• broken_links:
  • Can't resolve /zh-TW/docs/MDN/Community/Conversations#Chat_in_IRC
  • Can't resolve /zh-TW/docs/Learn/How_to_contribute
  • Can use the English (en-US) link as a fallback
  • Can use the English (en-US) link as a fallback
  • Can use the English (en-US) link as a fallback
  • and 39 more flaws omitted

External URLs

URL: /zh-TW/docs/Learn
Title: 學習該如何開發 Web
on GitHub

• https://discourse.mozilla-community.org/t/learning-web-development-marking-guides-and-questions/16294 (1 time) (Note! This may be a new URL 👀)
• https://exlskills.com/learn-en/courses (1 time) (Note! This may be a new URL 👀)