Fixed the issue for gesture's being added twice

1.Fixed the issue for gesture's being added twice:
When a push behaviour happens, the toVC add a gesture; when a pop behaviour happens, the toVC should remove the added gesture first, then add a new one. The old code just added gesture twice.
  
2.Removed unnecessary variable and `dealloc ` method:
`UIView` will remove all its gestures when dealloc automatically, so it's no need to remove the added gesture. Furthermore, the `CEBaseInteractionController` is used as a singleton, its `dealloc ` method will never get called.