Never show "I/O hunt" in menu when browsing sessions for a time slot

Previously the "I/O Hunt" menu item was shown unconditionally in the menu of the screen to browse sessions for one particular time slot. See here:

![iosched_io_hunt_menu_item](https://cloud.githubusercontent.com/assets/218061/4910992/e7286320-6486-11e4-9ed5-bcb796a296d8.png)

In my opinion the "I/O Hunt" menu item should never be shown in this screen like almost all of the menu items are not shown. So this pull request unconditionally removes it.