sync.profile: Point dependencies to an empty string

This means that we are going to use the same branch name for the
dependencies as the branch of the repository under test.

Change-Id: I6bf7bfaf03d8a999ed63167c487225eb7153a55a
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>