This variable doesn't exist on dora and will not break things.
Fixes:
ERROR: Please ensure module rtfifo is listed in KERNEL_MODULE_PROBECONF since module_conf_rtfifo is set
This has been fixed in upstream of OE-Core and in newer versions
of Yocto. For Edison provide our own version of the pkg_postinst
and pkg_postrm routines. It is not clear yet if this conflicts with
newer versions of poky but all that could happen is that the symlink
is changed twice and removed twice but the command ends with a || true
so this should not cause any kind of fault.