Remove non-latest symlink before creating
    
    This change can reduce crashing when symlink already exists.
    
    compose.pungi_compose_id generated in pungi is used for creating symlink
    but it's really hard to avoid creating same id with race condition.
    
    JIRA: RHELCMP-522
    Signed-off-by: Haibo Lin <hlin@redhat.com>