ipa-sidgen: fix memory leak in ipa_sidgen_add_post_op
    
    Also remove unused "search_pb" variable and its associated free
    functions.
    
    Fixes: https://pagure.io/freeipa/issue/9772
    Signed-off-by: Julien Rische <jrische@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>