re-enable flow check in github-build-check

Summary:
OSS CI has been marked as broken for a week or so due to a flow error but was just detected due to T189426364.

```
$ flow check
Error ----------------------------------------------------------------------------------------- flow-typed/react.js:39:6

Cannot resolve name `React$ElementFactory`. [cannot-resolve-name]

   39|   ): React$ElementFactory<ElementType>;
            ^^^^^^^^^^^^^^^^^^^^

```

OSS<>InternalFB inconsistencies  could be caught via the sandcastle job `github-build-check`. But `flow check` was purposefully disabled in 2021 in `github-build-check` due to a previous issue (D31590484).

This diff re-enables the `flow check` in `github-build-check` .

It also fixes the `flow` issue we were seeing in OSS CI by removing the deprecated [`createFactory`](https://react.dev/reference/react/createFactory) function from the flow-typed react module -- which we aren't currently using.

Reviewed By: gorodscy

Differential Revision: D57499258

fbshipit-source-id: 1a24cd276a71337af3d5ec05c43ab4d58ebd3243

flow-typed/react.js

@@ -34,9 +34,6 @@ declare module react {
   ): React$Context<T>;
   declare export var createElement: React$CreateElement;
   declare export var cloneElement: React$CloneElement;
-  declare export function createFactory<ElementType: React$ElementType>(
-    type: ElementType,
-  ): React$ElementFactory<ElementType>;
   declare export function createRef<T>(): {|current: null | T|};
 
   declare export function isValidElement(element: any): boolean;
@@ -219,7 +216,6 @@ declare module react {
     +createContext: typeof createContext,
     +createElement: typeof createElement,
     +cloneElement: typeof cloneElement,
-    +createFactory: typeof createFactory,
     +createRef: typeof createRef,
     +forwardRef: typeof forwardRef,
     +isValidElement: typeof isValidElement,