Remove function duplicate

[JoeSSS]

waitingForFile function is duplicated in two view controllers:

https://github.com/xing/calabash-launcher/blob/master/Launcher/Classes/ViewControllers/ElementConstructorViewController.swift#L56

https://github.com/xing/calabash-launcher/blob/master/Launcher/Classes/ViewControllers/InspectorViewController.swift#L196

The only difference between two is different UI element animation triggering.