CRAS: metrics - Use libmetrics instead of calling metrics_client

This change simplifies the seccomp policy file, by reducing
execve and a few other system calls.

BUG=chromium:871668
TEST=emerge adhd with chromeos-base/metrics side change,
verify events and samples can be sent to UMA.
CQ-DEPEND=CL:1163643,CL:1163644

Change-Id: I28290de0b9f670cdc5ad739823490061c0545f9a
Reviewed-on: https://chromium-review.googlesource.com/1163645
Commit-Ready: Hsinyu Chao <hychao@chromium.org>
Tested-by: Hsinyu Chao <hychao@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>
3 files changed