Remove broken links from USERS.md

[larsks]

I was looking for example sites and encountered several broken links in USERS.md. This commit removes all links that have connection problems. Links were verified using the script in 1.

A complete list of the removed links is included below.

• Removed https://thecodecousins.com: failed to connect
• Removed https://dawsonverboven.com/: failed to connect
• Removed https://geekx.tech/: failed to connect
• Removed https://ssgram.dev: failed to connect
• Removed https://schacherbauer.dev: failed to connect
• Removed https://waterloos.niflheimr.blue/: failed to connect
• Removed https://security.jtang.dev: ssl error (bad certificate?)
• Removed https://wjdevschool.com/: failed to connect
• Removed https://rinma.dev: ssl error (bad certificate?)
• Removed https://conight.com: 403 Client Error: Forbidden for url: https://conight.com/
• Removed https://markopolo123.github.io: 404 Client Error: Not Found for url: https://markopolo123.github.io/
• Removed https://openfoxblog.leven.dev/: ssl error (bad certificate?)
• Removed https://mickie1.gitlab.io/blog/: 503 Server Error: Service Temporarily Unavailable for url: https://gitlab.com/users/sign_in
• Removed https://cristiioan.me: ssl error (bad certificate?)
• Removed https://1mup.myorange.house: failed to connect
• Removed https://bg117.xyz/projects: failed to connect
• Removed https://nazdarthegame.com/: ssl error (bad certificate?)
• Removed https://dongzhi.me: 400 Client Error: Bad Request for url: https://dongzhi.me/