kdump-lib.sh: remove useless echo and cat
    
    upstream: fedora
    resolves: bz2003832
    conflict: none
    
    commit 53813e8b9af280315962ac6656318f94b1daf563
    Author: Kairui Song <kasong@redhat.com>
    Date:   Wed Sep 8 02:48:17 2021 +0800
    
        kdump-lib.sh: remove useless echo and cat
    
        Replace echo "$(cmd)" and "var=$(cmd); echo $var" with just `cmd`.
        And remove some useless cat.
    
        Signed-off-by: Kairui Song <kasong@redhat.com>
        Acked-by: Philipp Rudo <prudo@redhat.com>
    
    Signed-off-by: Tao Liu <ltao@redhat.com>