This arg used to be used in a 'sync' call that was removed in
crrev.com/7090f652, but it was never
applied to the remaining 'sync' call. This removes the arg and leaves
"--with_branch_heads" (and adds "--with_tags") as default sync flags.

Change-Id: Ice5a592d95a0b09dafddab24769f5edd8835a1c9
Recipe-Manual-Change: build_limited_scripts_slave
Recipe-Manual-Change: build
Reviewed-on: https://chromium-review.googlesource.com/677754Reviewed-by: Paweł Hajdan Jr. <phajdan.jr@chromium.org>
Commit-Queue: Michael Moss <mmoss@chromium.org>