Do not sync requirements to pbr

Syncing the requirements to pbr introduces a dependency on pip 1.4.
We don't actually require pip 1.4, and saying that we do breaks package
installation in a lot of cases.

Fixes-bug: #1296310
Change-Id: I69c67c4c8cba7076e33292eaab9070ba51b4dff3
Merge "Do not sync requirements to pbr"