remove useless dracut cmdline '-c /dev/null'

For "-c /dev/null" Harald mentioned that it is useless.
In fact, dracut code [[ -f /dev/null ]] will return false thus it will still use
the default config file

Signed-off-by: Dave Young <dyoung@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Cong Wang <amwang@redhat.com>

mkdumprd

@@ -13,7 +13,7 @@ SSH_KEY_LOCATION="/root/.ssh/kdump_id_rsa"
 SAVE_PATH=$(grep ^path $conf_file| cut -d' '  -f2)
 [ -z "$SAVE_PATH" ] && SAVE_PATH="/var/crash"
 extra_modules=""
-dracut_args=("--hostonly" "-c" "/dev/null" "-o" "plymouth dash")
+dracut_args=("--hostonly" "-o" "plymouth dash")
 
 add_dracut_arg() {
     while [ $# -gt 0 ];