jshell tool: line redrawn on each completion

Completions used to take place in-place. This was elegant. Now the line is always redrawn -- this amounts to three lines. If tabs are used frequently it is all you see on the screen.

For example typing "ArrayL<tab>" does the following:

    jshell> ArrayList
    ArrayList
   
    jshell> ArrayList

This is distracting, confusing, and verbose.

What it appears is that the behaviour which makes sense when there are multiple choices is being applied when there s only one choice.