Remove duplicate test (it's already in our functional tests)

This test duplicates what is here:
https://github.com/openstack/heat/blob/master/heat_integrationtests/functional/test_update.py#L89-L133

But does not require a full nested stack in unit tests.

Part of blueprint decouple-nested

Change-Id: If5a9d6b1c9dd98b31966312af16587cd148b9c6b
Merge "Remove duplicate test (it's already in our functional tests)"