Cirrus-CI: temporarily avoid qemu smoke test boot

Cirrus-CI has been red for some time because we're running out of disk
space on the ephemeral GCP VMs. For now remove the package + qemu boot,
and just check for build regressions.

This change to be reverted once we have identified and addressed the
underlying issue.

Sponsored by: The FreeBSD Foundation

(cherry picked from commit a7d593dd1da27833b5384349700bc3c7bcae6aad)