Revert install script back to the official location

[nohwnd]

dotnet-install script warns about not being able to check empty space on any powershell <7, which breaks our builds because any warning or error is listed as error.

I've used the script from main, where it is fixed on main and rel/17.7:

#4669
https://github.com/microsoft/vstest/pull/4668/files

Revert the changes to that file once the script is fixed.