Summary:
First part of the codegen script cleanup effort. Everything that was done in generate-specs.sh is now part of the CocoaPods recipe (e.g. codegen method in `react_native_pods.rb`).
Now that `generate-specs.sh` has been removed, the codegen may still be invoked manually for test purposes like so:
```
cd react-native
# Generate Schema - do this whenever your JS specs change
node packages/react-native-codegen/lib/cli/combine/combine-js-to-schema-cli.js <output_file_schema_json> <javascript_sources_dir>
# Generate native interfaces for iOS (use schema.json generated by previous step)
node scripts/generate-specs-cli.js ios <output_file_schema_json> <output_dir> <library_name>
```
Changelog: [Internal]
Reviewed By: fkgozali
Differential Revision: D30648067
fbshipit-source-id: 29688e0aac5496886657db82becb05bc8da076c9
ef6ad1f2d6