Remove hardcoded version.

API clients generally use semantic versioning, not pbr's pre-version facility
which is used for the API servers. This line causes local package builds to
have the wrong version (2.0.dev.. when 2.0 was released a long time ago) and
pbr will in future detect this and error.

Change-Id: Ief099a077f0c4da656dcdba10d86531694fc8491