fix: removes modern features from index

[rheh]

Index file should not use new language features as it must work on Node 0.10+ (as stated in index header). This fixes node 4 and below. This has been verified using nvm to switch versions; running the script on each version to assert the index runs correctly runs on all versions of node.

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Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Meta Open Source project. Thanks!