Summary:
NavigationState is composed of many things such as `index`, `routes`.
The only way to effectively compare navigation states is to assume their immutability
and simply compare their references.
That said, `navigationState.key` does not really serves anything useful. The key does
not make a navigation state more unique or comparable.
This diff makes `navigationState.key` irrelevant thus we could make NavigationState
simpler.
Reviewed By: ericvicenti
Differential Revision: D3351915
fbshipit-source-id: 75d5fa432d2a693f999a91b11e3bff1fdd42e61d
f7279b4074