fix(jest/setup): fix circular dependencies in mockModal (facebook#32964)

Summary:
Fixes facebook#32939
It appears there is circular dependencies on the Modal component that causes the modalMock function to be an empty object. Removing the import fixes the issue.
I don't know yet why this is not happening when executing the test suite inside `Modal-test.js` but I will investigate this later.

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[General] [Fixed] - Fix error "mockModal is not a function"

Pull Request resolved: facebook#32964

Test Plan:
On a newly initiated project using react-native 0.67.1 I created a ModalComponent:
```
import React from 'react';
import {Modal, Text} from 'react-native';

export const ModalComponent = () => {
  return (
    <Modal visible>
      <Text>Test</Text>
    </Modal>
  );
};
```
and a ModalComponent.test.tsx:
```
import 'react-native';
import React from 'react';
import {ModalComponent} from '../ModalComponent';

// Note: test renderer must be required after react-native.
import renderer from 'react-test-renderer';

it('renders correctly', () => {
  renderer.create(<ModalComponent />);
});
```

Running the test throws the error "TypeError: mockModal is not a function".

After modifying the mockModal inside node_modules/react-native/jest/mockModal.js it works correctly.

Reviewed By: christophpurrer

Differential Revision: D33771136

Pulled By: lunaleaps

fbshipit-source-id: c09ada8d2f864f5568b3379616a6cace9fb9921e

Author: AntoineDoubovetzky

jest/mockModal.js

@@ -13,11 +13,11 @@
 'use strict';
 
 const React = require('react');
-const Modal = require('../Libraries/Modal/Modal');
+import typeof Modal from '../Libraries/Modal/Modal';
 
 function mockModal(BaseComponent: $FlowFixMe) {
   class ModalMock extends BaseComponent {
-    render(): React.Element<typeof Modal> {
+    render(): React.Element<Modal> {
       return (
         <BaseComponent {...this.props}>
           {this.props.visible !== true ? null : this.props.children}