Delete obsolete MountingIntermediateCommits-itest.js (#56628)

Summary:
Pull Request resolved: #56628

This test file contains a single `it.skip` test guarded by the comment "Enable once synchronous C++ state updates are re-introduced." That feature was deleted entirely (not just disabled) since 2025-07-15, with the reason: *"The current design of enableSynchronousStateUpdates is not correct and breaks `<Modal />` on Android. let's delete it.

Findings: A scan of `packages/react-native/src/private/featureflags`, `scripts/featureflags`, and `ReactCommon/react/featureflags` returns no replacement flag for synchronous C++ state updates. The `enableSynchronousStateUpdates` flag was removed from every layer (JS config, C++, Android Kotlin/JNI, iOS overrides, MC schemas) and the guarded code path in `EventQueue.cpp` was deleted as well.

Empirical confirmation: Removed the `it.skip` and ran the test 10x via stress runs. All 10 runs failed deterministically. The test is asserting the *presence* of the bug — i.e., that an intermediate state mutation leaks through when a UI-thread commit pulls transactions from an in-flight JS commit. Without the synchronous-state-updates codepath, that leak no longer occurs, so the test's expected log never matches the actual output:

  Expected: [Update ScrollView, Update intermediate-state-should-not-be-visible, Update view]
  Actual:   [Update view, Update ScrollView]

The test cannot be un-skipped (the bug it documents is no longer reproducible), and rewriting the assertion would defeat the purpose of the test. Deleting it.

Changelog: [Internal]

Reviewed By: pixelfreak

Differential Revision: D102661539

fbshipit-source-id: fca5d552a80cad572ac43047ff6709403de294f1

Author: fkgozali