Update Site index.html having incorrect prerequsites

## Summary

When running with the **SAP BTP Cloud Trial**, the prerequisites are incorrect. A local _abapGit_ installation is not required and the _ADT_Backend_ is archived if I'm not mistaken.

## Possible Solution

Either have separate prerequisites when running with the on-premise SAP installation or the cloud installation.
Remove the incorrect links to _ADT_BACKEND_.