Remove bazel sync from Dockerfile. (#4669)
Remove bazel sync from Dockerfile. (#4669)

With caching and not downloading unnecessary binaries, it still seems
faster to fetch repos on demand.
PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs