Remove "Dashboard" from the `Kill affected applications` section

`killall Dashboard` doesn't actually do anything. To apply the changes for Dashboard, `killall Dock` is enough as Dock is Dashboard's parent process.

![screen shot 2013-11-03 at 12 56 03 am](https://f.cloud.github.com/assets/1223565/1460135/275a03a8-4413-11e3-89dc-8ff98ebc8265.png)