Remove USE flag cros_host from system_api

USE flag cros_host is removed because it is not used
in system_api source code but introduces dependency on net-libs/grpc.
Disabling the use flag in package.provided is overwirtten
when building SDK, so we need to remove it direcly.

BUG=b/340935901
TEST=presubmit
RELEASE_NOTE=None

Change-Id: I8ad40f8697ab49ea7fda0888f6938d600cc29df8
Reviewed-on: https://cos-review.googlesource.com/c/third_party/overlays/chromiumos-overlay/+/74216
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
2 files changed