sys-kernel: remove 5.15 kernel package

BUG=b/353766553
TEST=presubmit, validation
RELEASE_NOTE=None

Change-Id: Ic9ef83bc0494dbf4302cae1186428761439693f0
Reviewed-on: https://cos-review.googlesource.com/c/cos/overlays/board-overlays/+/76800
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Oleksandr Tymoshenko <ovt@google.com>
11 files changed