net/af_xdp: remove unused Tx counter
net/af_xdp: remove unused Tx counter

This Tx counter is now unused.

Fixes: 10edf857fde4 ("net/af_xdp: make reserve/submit peek/release consistent")
Cc: stable@dpdk.org

Signed-off-by: David Marchand <f28529695cfa9e3e1eb84e7072aa626af4abb18e@redhat.com>
Reviewed-by: Xiaolong Ye <c7d6fc2f7e22da80deb234d523238b510a8c0f08@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk