Remove broken Medium links from JavaScript section

[fengfeng-zi]

Summary

• remove the broken Medium tutorial link for \Build an App in Pure JS\
• remove the broken Medium tutorial link for \Build a TicTacToe Game with JavaScript\
• keep the JavaScript section limited to working resources

Fixes #836

[tuvtran]

Thanks — you were right that both Medium links are dead (they now return 410 Gone), and I've removed them from the JavaScript section in commit 2554640. I left out the new resource-tag convention, since changing the entry format across CONTRIBUTING.md and the README is a bigger maintainer decision than this fix needed. Appreciate you following up on #836!