SDAP: remove duplicated code
    
    Body of functions sdap_x_deref_search_done(), sdap_asq_search_done(),
    sdap_sd_search_done and sdap_get_generic_done() are the same. Remove
    code duplication by calling sdap_get_generic_done() from
    sdap_x_deref_search_done(), sdap_sd_search_done and from
    sdap_asq_search_done() instead of having two more duplicate
    implementations.
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>