Remove unreferenced react-native-host-hooks from flow (facebook#27457)

## Summary

These modules are no longer referenced in the React codebase. We should
remove them to limit the API surface area between React and React
Native.

## How did you test this change?

`yarn flow native && yarn flow fabric`

scripts/flow/react-native-host-hooks.js

@@ -230,33 +230,3 @@ declare var nativeFabricUIManager: {
   unstable_getCurrentEventPriority: () => number,
   ...
 };
-
-declare module 'View' {
-  declare module.exports: typeof React$Component;
-}
-
-declare module 'RTManager' {
-  declare function createNode(
-    tag: number,
-    classType: string,
-    props: ?Object,
-  ): void;
-
-  declare function beginUpdates(): void;
-
-  declare function appendChildToContext(
-    contextTag: number,
-    childTag: number,
-  ): void;
-  declare function appendChild(parentTag: number, childTag: number): void;
-  declare function prependChild(childTag: number, beforeTag: number): void;
-  declare function deleteChild(childTag: number): void;
-  declare function updateNode(tag: number, props: ?Object): void;
-
-  declare function completeUpdates(): void;
-}
-
-// shims/ReactFeatureFlags is generated by the packaging script
-declare module '../shims/ReactFeatureFlags' {
-  declare export var debugRenderPhaseSideEffects: boolean;
-}