Update Array extensions for Swift 2.0.
Update Array extensions for Swift 2.0.

`contains` is now a part of `Array` by default, so this version isn't
necessary. `remove` is a good addition, but the previous version didn't
type-check the element to remove.

insidegui/WWDC,SoneeJohn/WWDC,MaddTheSane/WWDC,SoneeJohn/WWDC,natecook1000/WWDC,insidegui/WWDC,insidegui/WWDC,insidegui/WWDC