Remove flow libdefs from npm package (#51556)

Summary:
Pull Request resolved: #51556

Excludes `packages/react-native/flow/` from being published to npm.

**As far as I know**, we already axed open source Flow support with a similar change in D46313482 (Jun 2023).

Changelog:
[General][Breaking] - The `react-native` package no longer ships with the `flow` directory

Reviewed By: cipolleschi

Differential Revision: D75060845

fbshipit-source-id: 3cb81820499383bf095abc97a9ab7e9061c870d6

Author: huntie

packages/react-native/package.json

@@ -74,7 +74,6 @@
   "files": [
     "build.gradle.kts",
     "cli.js",
-    "flow",
     "gradle.properties",
     "gradle/libs.versions.toml",
     "index.js",