Delete redundant test for on atom.onUpdateAvailable

This test emitted an event in the main process, which caused exceptions 
in all *other* Atom windows 🙀.

spec/atom-environment-spec.js

@@ -746,29 +746,6 @@ describe('AtomEnvironment', () => {
     })
   })
 
-  describe('::updateAvailable(info) (called via IPC from browser process)', () => {
-    let subscription
-
-    afterEach(() => {
-      if (subscription) subscription.dispose()
-    })
-
-    it('invokes onUpdateAvailable listeners', async () => {
-      if (process.platform !== 'darwin') return // Test tied to electron autoUpdater, we use something else on Linux and Win32
-
-      const updateAvailablePromise = new Promise(resolve => {
-        subscription = atom.onUpdateAvailable(resolve)
-      })
-
-      atom.listenForUpdates()
-      const {autoUpdater} = require('electron').remote
-      autoUpdater.emit('update-downloaded', null, 'notes', 'version')
-
-      const {releaseVersion} = await updateAvailablePromise
-      expect(releaseVersion).toBe('version')
-    })
-  })
-
   describe('::getReleaseChannel()', () => {
     let version