mkdumprd: Improve the config reading logic

Seems some dead codes are left here for historical reason, just remove
them, read the config and strip comments only for once.

This improve the speed by a lot (2.6s -> 0.498s for reading a
simple config in my test case, on HDD) and make the code cleaner.

Signed-off-by: Kairui Song <kasong@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>

mkdumprd

@@ -444,13 +444,9 @@ do
         add_dracut_arg $config_val
         ;;
     *)
-        if [ -n $(echo $config_opt | grep "^#.*$") ]
-        then
-            continue
-        fi
         ;;
     esac
-done < $conf_file
+done <<< "$(grep -v -e "^#" -e "^$" $conf_file)"
 
 handle_default_dump_target