[BUGFIX] Extension Manager: Change the cursor on hover of required extensions

The new extension manager shows the "hand" cursor when hovering over
the icon of a required extension. This change just disables that by
enforcing the browser to show the default "arrow" cursor.

Change-Id: I05c075710effb9de3de147ba716495362c39da0a
Resolves: #13267
Releases: 4.6
Reviewed-on: http://review.typo3.org/3463
Reviewed-by: Christopher 
Tested-by: Christopher 
Reviewed-by: Stefan Neufeind
Reviewed-by: Steffen Gebert
Tested-by: Steffen Gebert