The cargo interaction with the .cargo/config does not meet our
requirements.
Regardless of .cargo/config explicitly replacing our external sources
with vendored ones, cargo build will rely first on Cargo.lock to update
its local source cache. If a dependency has been push forced, build
fails because of our top level Cargo.toml description.
This prevents us from actually pinning dependencies, which defeats the
vendoring purpose.
We're removing vendoring for now, until we understand it better.
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>