Upgrade which / simplify use

Summary:
It's already a promise. With the next upgrade this otherwise causes
some nasty type errors due to overloading.

Reviewed By: jknoxville

Differential Revision: D18059641

fbshipit-source-id: 93cee95d7bbf767ff6276a0946262bf83587c728

src/chrome/DevicesButton.tsx

@@ -13,15 +13,12 @@ import {spawn} from 'child_process';
 import {dirname} from 'path';
 import {selectDevice, preferDevice} from '../reducers/connections';
 import {default as which} from 'which';
-import {promisify} from 'util';
 import {showOpenDialog} from '../utils/exportData';
 import PropTypes from 'prop-types';
 import BaseDevice from '../devices/BaseDevice';
 import React, {Component} from 'react';
 import {State} from '../reducers';
 
-const whichPromise = promisify(which);
-
 type StateFromProps = {
   selectedDevice: BaseDevice | null | undefined;
   androidEmulators: Array<string>;
@@ -48,7 +45,7 @@ class DevicesButton extends Component<Props> {
   launchEmulator = (name: string) => {
     // On Linux, you must run the emulator from the directory it's in because
     // reasons ...
-    whichPromise('emulator')
+    which('emulator')
       .then(emulatorPath => {
         if (emulatorPath) {
           const child = spawn(emulatorPath, [`@${name}`], {