EventEmitter: Cleanup Redundant Internal Types
EventEmitter: Cleanup Redundant Internal Types

Summary:
Cleans up some minor redundant internal types in `_EventEmitter.js`.

Changelog:
[Internal]

Reviewed By: rubennorte

Differential Revision: D27712301

fbshipit-source-id: e6affcb7948e0f47a1775b74b12f59ec2a6abddb

pandiaraj44/react-native,facebook/react-native,pandiaraj44/react-native,pandiaraj44/react-native,facebook/react-native,javache/react-native,facebook/react-native,janicduplessis/react-native,javache/react-native,javache/react-native,javache/react-native,javache/react-native,janicduplessis/react-native,pandiaraj44/react-native,facebook/react-native,arthuralee/react-native,arthuralee/react-native,facebook/react-native,myntra/react-native,janicduplessis/react-native,arthuralee/react-native,myntra/react-native,pandiaraj44/react-native,javache/react-native,janicduplessis/react-native,myntra/react-native,myntra/react-native,pandiaraj44/react-native,janicduplessis/react-native,pandiaraj44/react-native,facebook/react-native,pandiaraj44/react-native,myntra/react-native,facebook/react-native,janicduplessis/react-native,myntra/react-native,javache/react-native,javache/react-native,myntra/react-native,facebook/react-native,janicduplessis/react-native,janicduplessis/react-native,javache/react-native,myntra/react-native,arthuralee/react-native,arthuralee/react-native,facebook/react-native,myntra/react-native