CentOS/RHEL replaced yum by dnf and yum is no longer available by
default. We (and the other projects) updated implementations to adapt
that change so we assume we no longer need the old yum command (which
is just an alias of dnf).
Depends-on: https://review.opendev.org/884307
Change-Id: I5152d1013a603e8d230748ff956d33507675450c