Why? The test suite that uses it is responsible for setting up the stub in it's `setup` function.  If the method is already a sinon stub, it then complains when inside the setup I try to stub it again.

This should just be a no-op hanging point to allow you to stub it in the test suite ala https://github.com/mozilla-b2g/gaia/pull/12866/files#diff-9ea1ebee4e3ce5def54dd7fdc8b9a65bR172