selftests: netfilter: nft_concat_range.sh: drop netcat support

Tests fail on my workstation with netcat 110, instead of debugging+more
workarounds just remove this.

Tests will fall back to bash or socat.

Signed-off-by: Florian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/r/20240423130604.7013-3-fw@strlen.de


Signed-off-by: Jakub Kicinski <kuba@kernel.org>