Fix js-flipper tests (#3297)

Summary: Pull Request resolved: https://github.com/facebook/flipper/pull/3297

Reviewed By: passy

Differential Revision: D33619287

fbshipit-source-id: 7e9dc595c999e9c8b61329f96adba6e45a1dfa50

js/js-flipper/src/util.ts

@@ -66,5 +66,3 @@ export const detectDevice = (): string => {
   }
   return require('os').release();
 };
-
-export const awaitTimeout = (timeout: number) => new Promise(resolve => setTimeout)