No Pointer style cursor for table head when no hint or sorting (#910)

* No Pointer style cursor when no hint or sorting

With no sorting or a hint, the cursor still shows a pointer. I'm not saying this is the best solution, but I think the header shouldn't shouldn't show a pointer style of cursor when there is nothing to click on or additional behavior from hovering.

* Update TableHeadCell.js

src/components/TableHeadCell.js

@@ -167,7 +167,7 @@ class TableHeadCell extends React.Component {
             </span>
           </Tooltip>
         ) : (
-          <div className={classes.sortAction}>
+          <div className={hint ? classes.sortAction : null}>
             {children}
             {hint && (
               <Tooltip