Regression in dex split for non predexed apps

Created by: kageiit

isAllowRDotJavaInSecondaryDex in AndroidGraphEnhancerArgs needs to be defaulted to true.

This commit https://github.com/facebook/buck/commit/8c331339d4484f90c8888db175af805887a01015 broke apps that have a large number of R classes . This is a regression and can affect any apps in the wild using buck. The previous behavior should be the default to prevent this from happening.

cc @dreiss @styurin