Fix more tests

Summary: beeper node modules has a `return` statement outside of a function which doesn't parse. To fix it, we mock it. Also, setupEnvPolyfills is no longer being used.
Closes https://github.com/facebook/react-native/pull/2770

Reviewed By: @​svcscm

Differential Revision: D2448882

Pulled By: @vjeux

local-cli/__mocks__/beeper.js

@@ -0,0 +1,5 @@
+// beeper@1.1.0 has a return statement outside of a function
+// and therefore doesn't parse. Let's mock it so that we can
+// run the tests.
+
+module.exports = function () {};