NavigationButtonView: remove redundant onchange from setting observer, and prevent double (un)registration.

Change-Id: I05de2946823647345e34ced6c3b4394afecb22f4
This ain't no superclass method.

Change-Id: I8f60c93a088068b34bc023766657ba050dc11ec1
No need this twice

This reverts commit 52d25be8886ccebd854fb1d0c8e86501cad130f1.

Change-Id: I011c39d970ad4587ea527aadf32a5a79040f80c5
For Lokesh ;)

Change-Id: Id59f9c156f0dd47b5248267f8d75862cc103a10e