7.3 Portal Forms - How can we remove the default "next" and "prev

For Portal tasks CSS would do the trick. You can apply styles to each button depending on the label it has. For instance:

input[value='myNextButton']{          
          background-color:#225533 !important;
          color:#FFFFFF !important;
}

input[value='Previous']{          
          background-color:#002654 !important;
          color:#FFFFFF !important;
}

input[value='Third button']{          
          background-color:#44bbcc !important;
          color:#FFFFFF !important;
}

In this example, I labeled my submit button as: "myNextButton", the previous button is always labeled "Previous" and I have another button labeled as "Third button" that is why I put that in my CSS in the value search criteria. Notice how these are the labels of the button and NOT the ID.

You could simply add

display:none !important;