Improvement : Remove warning while running tests

[mfrachet]

When running tests, we got warning like :

est-haste-map: duplicate manual mock found:
  Module name: ReactNative
  Duplicate Mock path: /Users/pc/Soft/rnUx/Example/node_modules/react-native/Libraries/Renderer/src/renderers/native/__mocks__/ReactNative.js
This warning is caused by two manual mock files with the same file name.
Jest will use the mock file found in:
/Users/pc/Soft/rnUx/Example/node_modules/react-native/Libraries/Renderer/src/renderers/native/__mocks__/ReactNative.js
 Please delete one of the following two files:
 /Users/pc/Soft/rnUx/node_modules/react-native/Libraries/Renderer/src/renderers/native/__mocks__/ReactNative.js
/Users/pc/Soft/rnUx/Example/node_modules/react-native/Libraries/Renderer/src/renderers/native/__mocks__/ReactNative.js

or

 console.error node_modules/fbjs/lib/warning.js:36
Warning: ReactTestUtils has been moved to react-dom/test-utils. Update references to remove this warning.

Would be great to avoid that :)