Remove slack link in Czech translation

[Roshanjossey]

🐞 Problem
We're moving away from using slack

🎯 Goal
Have no links to slack

💡 Possible solutions
Remove link to slack in Czech translation.
You can find it in https://github.com/firstcontributions/first-contributions/blob/main/docs/translations/README.cs.md?plain=1#L2

Important

Please only address one issue in a PR.
Let's make it possible for more people to solve issues here.

📋 Steps to solve the problem

• Comment below about what you've started working on.
• Add, commit, push your changes.
• Submit a pull request and add this in comments - Addresses #<put issue number here>
• Ask for reviews in comments section of pull request.
• Celebrate your contribution to this project. 🎉

[murtazajoo]

Can I do it?

[Roshanjossey]

sure

[Carlvensky]

I'm working on it. I didn't find another link to replace the Slack link for when they need help.

V případě, že byste měli jakékoliv otázky nebo potřebovali pomoct, můžete se [přidat k našemu Slack teamu](https://join.slack.com/t/firstcontributors/shared_invite/zt-1hg51qkgm-Xc7HxhsiPYNN3ofX2_I8FA).