Summary:
Upgrades dependents of `EventEmitter`, `EventSubscription`, `EventSubscriptionVendor`, and `EmitterSubscription` to use `import` instead of `require`.
Changelog:
[Internal]
(Note: this ignores all push blocking failures!)
Reviewed By: cpojer
Differential Revision: D22182312
fbshipit-source-id: e9444aa2728d89d52f577725f688871f7dbfba8a