This removes the entire relationship between an instance and the flavor it was created from. As such, it removes two tests entirely which examined the old behavior. This is one change in a series aimed at removing the use of instance-linked instance_type objects, in favor of the decoupled type data in system_metadata. See bug 1140119 for more details. Change-Id: I8b525a900bf2dc6b193e54aae35fc32248e4cff4