feat(grid): remove viewportIndex and only rely on viewportId (#3591)

Co-authored-by: Bill Wallace <wayfarer3130@gmail.com>

extensions/_example/src/index.js

@@ -121,7 +121,7 @@ const getSopClassHandlerModule = (/* ... */) => {
 
 const getToolbarModule = () => {};
 
-// displaySet, viewportIndex, dataSource
+// displaySet, dataSource
 const getViewportModule = () => {
   const wrappedViewport = props => {
     return (