ad: remove subdomain that has been disabled through ad_enabled_domains from sysdb
    
    If previously enabled subdomain was disabled by removing it from ad_enabled_domains
    option in sssd.conf, its cached content (including the domain object itself)
    was kept in sysdb. Therefore eventhough the domain was effectively disabled in
    backed its cached data was still available in responders.
    
    Subdomains that are disabled on server side are correctly removed from sysdb in
    `ad_subdomains_refresh()` so this issue is related only to the configuration
    option.
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/4009
    
    Reviewed-by: Sumit Bose <sbose@redhat.com>
    (cherry picked from commit 815957cd10a82aca6742b0bd56c7e7f199596cd4)