Documentation: Host challenge: Fix duplication

[AyushR1]

In docs/source/host_challenge.md the paragraph "We support two types of code-upload-based challenges..." is repeated twice. This repetition can be confusing for readers,

To improve clarity, one of the sentences should be removed.

[Ru28]

Hi @AyushR1 can I work on this issue but I am beginner to this project so if it is good to start.

[Dedeepya-K]

Hey there, as a part of GSoC even I would like to contribute and if the issue is still open and no one is working on it, I would like to take this up.