"rnpm" deprecation warnings encourage library to not be backwards compatible

[thymikee]

Description

If a package defines both "rnpm" key in package.json and a react-native.config.js file, we still produce warnings:

cli/packages/cli/src/tools/config/index.js

Lines 41 to 43 in 29ae253

	config =
	readLegacyDependencyConfigFromDisk(root) ||
	readDependencyConfigFromDisk(root);

I don't think this is what we want, because if a package wants to get rid of the warning, they'll need to remove "rnpm" entry and in turn bump major version, becoming only compatible with RN 0.60+.

We need to swap the order of loading deps and handle it accordingly.

[grabbou]

Good catch. We should have a check before doing it. I'll move warn to be printed in index.js, instead of inside readLegacyDependencyConfigFromDisk and that will solve it :)