Delete interface.js (Flow), relocate __DEV__ global (#57275)

Summary:

`interface.js` was a legacy, Flow-only entry point whose sole content was a bare `declare var __DEV__: boolean;` global, registered as a Flow `[libs]` file.

Relocate into `flow/globals.js`, allowing us to drop this from the package `"files"` (and `"exports"`) list.

Changelog: [Internal]

Differential Revision: D109018822

Author: huntie

.flowconfig

@@ -39,7 +39,6 @@
 
 [libs]
 flow-typed/
-packages/react-native/interface.js
 packages/react-native/flow/
 
 [options]

packages/react-native/flow/global.js

@@ -86,3 +86,6 @@ declare var global: {
   // Undeclared properties are implicitly `any`.
   [string | symbol]: any,
 };
+
+// __DEV__ is additionally declared as a bare global
+declare var __DEV__: boolean;

packages/react-native/interface.js

@@ -80,7 +80,6 @@
     "gradle/libs.versions.toml",
     "index.js",
     "index.js.flow",
-    "interface.js",
     "jest-preset.js",
     "Libraries",
     "LICENSE",