create-spdx: delete virtual/kernel dependency to fix FreeRTOS build

When building FreeRTOS this dependency generates an error because
bitbake cannot find any provider for "virtual/kernel".
From a dependency analysis the task is executed indipendently from
this so it can be safely removed.

This patch has been discussed in this ML thread:
https://lists.openembedded.org/g/openembedded-core/topic/90602531

Upstream-Status: Submitted
https://lists.openembedded.org/g/openembedded-core/message/164876



Signed-off-by: Davide Gardenal <davide.gardenal@huawei.com>