chrome-base: Remove key_reader dependencies for cros_host.

Add xkb dependencies only when needed.

BUG=none
TEST=emerge-hatch chromeos-installer

Change-Id: Ie66755682cbf4b3d9b769ec5152f217f431570cf
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2593694
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Tested-by: Vyshu Khota <vyshu@google.com>
Commit-Queue: Vyshu Khota <vyshu@google.com>
1 file changed