Remove slack link in Dutch translation

[Roshanjossey]

🐞 Problem We're moving away from using slack

🎯 Goal Have no links to slack

💡 Possible solutions Remove link to slack in Dutch translation. You can find it in https://github.com/firstcontributions/first-contributions/blob/main/docs/translations/README.nl.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 #'
• Ask for reviews in comments section of pull request.
• Celebrate your contribution to this project. 🎉

[Rohanssutar]

Hi, I am working on this issue.

[Rohanssutar]

I've removed the slack link in Dutch translation. Please review the PR.

[Esh07]

I've removed the slack link in Dutch translation. Please review the PR.

I can see your PR #104944. However, you'd deleted head branch before even it get merged to repo