Only rely on developer option for back animation

BackNavigationController was still relying on a debug setting. Now the
animation request is handled via a boolean parameter passed by sysui,
which has access to the developer option.

Test: Existing test modified
Bug: 231502692
Change-Id: Icda4692e05396407d961610de0ce709492adadc1
Merged-In: Icda4692e05396407d961610de0ce709492adadc1