conf: Drop unnecessary caps parsing logic

conf: Drop unnecessary caps parsing logic

The comment says:

    /* If the logic here seems fairly arbitrary, that's because it is :)
     * This is duplicating how the code worked before
     * CapabilitiesDomainDataLookup was added. We can simplify this,
     * but it would take a bit of work because the test suite fails
     * in numerous minor ways. */

Nowadays the test suite changes appear quite simple, just extending
test capabilities data a bit so that we aren't trying to define
invalid arch/os/virtType/machine combos

Acked-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Cole Robinson <crobinso@redhat.com>