Drop e2fsprogs scratch build workaround
    
    Drop the e2fsprogs scratch build workaround we were using for
    https://github.com/fedora-silverblue/issue-tracker/issues/470 -
    with the new 'use a custom ref and rebase to the official ref'
    thing I implemented for update ostree tests, it shouldn't be
    necessary any longer.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>