Never mind, I found it by looking at tootipOptions in the debug mode to say totalLength: false. However, it seems the documentation of visibleElements property is missing.
In addition, I see there are few issues as well.
1) tooltip doesn't display if the activeTool is 'rectangle' or 'circle' or 'point' or 'multipoint'.
2) tooltip text is wrong if the mode: 'freehand' is selected. It displays 'Click on the map to start drawing'. However, it needs to be dragged to start drawing in this mode. Similar way, it's wrong tooltip text while ending the drawing in this mode.
Can anyone from ESRI confirm if these are already known bugs or any workarounds?