buffet: stop linking against libmetrics BUG=None TEST=emerge-amd64-generic --unmerge metrics && emerge-amd64-generic buffet works. Change-Id: I45d46b0a335d0d71c8dc6f57404b887d6cfe0488 Reviewed-on: https://chromium-review.googlesource.com/214756 Reviewed-by: Alex Vakulenko <avakulenko@chromium.org> Tested-by: Bertrand Simonnet <bsimonnet@chromium.org> Commit-Queue: Bertrand Simonnet <bsimonnet@chromium.org>