Summary:Given that you can do all kinds of animations other than `Animated.timing`, it made no sense to have `setTiming`. In addition, you can't intuitively tell that this is the callback where you would do custom animations.
The discussion took place on Discord with ericvicenti: https://discordapp.com/channels/102860784329052160/154015578669973504
Closes https://github.com/facebook/react-native/pull/6235
Differential Revision: D2999121
Pulled By: hedgerwang
fb-gh-sync-id: f587b865de11ba5e8dc9c430720252ffb5d12794
shipit-source-id: f587b865de11ba5e8dc9c430720252ffb5d12794