dracut-kdump.sh: remove add_dump_code
    
    upstream: fedora
    resolves: bz2003832
    conflict: none
    
    commit 8f89e890713c382c88a7e00420ef3b98c2dc708d
    Author: Kairui Song <kasong@redhat.com>
    Date:   Mon Aug 2 01:25:17 2021 +0800
    
        dracut-kdump.sh: remove add_dump_code
    
        `add_dump_code "<op>"` is just `DUMP_INSTRUCTION="<op>"`, no need a
        extra wrapper for that.
    
        Signed-off-by: Kairui Song <kasong@redhat.com>
        Acked-by: Philipp Rudo <prudo@redhat.com>
    
    Signed-off-by: Tao Liu <ltao@redhat.com>