Drop 'SUBVARIANT_OR_ARM' replacement, enable aarch64 in checkwiki
    
    I'm planning to enable aarch64 testing in openQA prod. This is
    part of the groundwork. We 'enable' aarch64 in checkwiki, i.e.
    check wiki result submission concordance with the test templates
    and the wiki matrix templates for aarch64 as well as x86_64. I
    made some changes to the matrix templates themselves at the same
    time which mean checkwiki now almost passes, and I mean to make
    some changes to the test templates that will fix the remaining
    issue. We make one small change to the test suite config here to
    match a change made in the wiki.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>