Remove Polyfills from RN Open Source

Summary:
We don't need these polyfills in RN Open Source any longer because JSC supports these features natively.

We also don't need these internally at FB, but I want the removal to be a step by step process and separate from the open source work.

Reviewed By: rickhanlonii

Differential Revision: D14762827

fbshipit-source-id: 114626bd18516c42ced43c3f7aa29d42d1d95335

Author: cpojer