Use jest to mock electron in tests

Summary:
Replacing our custom electron-stubs transform with a mocked module.

This will now be the default impl for tests, and we can override it by mocking as needed.

Reviewed By: passy

Differential Revision: D17979659

fbshipit-source-id: a26994158d439fa7dc1ca38225294106fc4e1559

__mocks__/electron.tsx

@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+module.exports = {
+  remote: {
+    process: {
+      env: {},
+    },
+    app: {
+      getAppPath: process.cwd,
+      getVersion: () => '0.9.99',
+      relaunch: () => {},
+      exit: () => {},
+    },
+    getCurrentWindow: () => ({isFocused: () => true}),
+  },
+};