Remove unused Promise polyfill and promise dependency

[aravi365]

Summary

Fixes #57702.

polyfillPromise.js falls back to require('../Promise') when
HermesInternal.hasPromise() is falsy. That require is statically reachable, so
Metro bundles the promise package into every app even though Hermes apps never
execute it. Removing the fallback drops the dependency and the dead code from the
bundle.

This removes:

• the polyfill branch in polyfillPromise.js
• Libraries/Promise.js
• the promise dependency and its flow-typed def

DEV unhandled-rejection tracking is unchanged, it goes through
HermesInternal.enablePromiseRejectionTracker. promiseRejectionTrackingOptions.js
imported its options type from promise/setimmediate/rejection-tracking, so that
type is now declared inline.

One thing worth a maintainer's call: the fallback also covered non-Hermes engines
(JSC, V8), which now get the engine's native Promise instead. Both ship a
spec-compliant implementation today, and the "Event loop not supported" comment
this code was written for no longer applies, but if you'd rather keep the polyfill
for those engines I can gate it instead of deleting it.

Changelog:

[GENERAL] [REMOVED] - Remove the unused Promise polyfill and the promise dependency

Test Plan

• git grep finds no remaining references to Libraries/Promise or
  promise/setimmediate in the repo.
• Only the promise line is removed from package.json.
• Behaviour on Hermes is unchanged: hasPromise() is true, so global.Promise
  was already the one in use, and the DEV rejection tracker still gets the same
  options object.

I have not run the full JS suite locally, relying on CI for test_js, Flow and lint.

[meta-codesync]

@robhogan has imported this pull request. If you are a Meta employee, you can view this in D114354694.