Remove SoftDeletingTrait from User model

Since Orchestra/Model/User has already import the SoftDeletingTrait trait, importing it again in User model will throw an exception.

![orchestra](https://cloud.githubusercontent.com/assets/4233863/3363150/f5997cbc-fb10-11e3-85bf-a591482701c7.jpg)

Signed-off-by: Ahmad Shah Hafizan Hamidin <ahmadshahhafizan@gmail.com>