app/testpmd: fix cleanup of Tx metadata offload

app/testpmd: fix cleanup of Tx metadata offload

Commit in fixes tag removed the match_metadata Tx offload.
This patch removes the option to select this offload from testpmd
menu, help text and documentation.

It also modifies the cmd_show_tx_metadata_parsed() function, to
display the value correctly, and the dump_pkt_burst() function to
display the relevant (Tx/Rx) metadata only.

Fixes: 9bf26e1318e3 ("ethdev: move egress metadata to dynamic field")

Signed-off-by: Dekel Peled <dekelp@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Bernard Iremonger <bernard.iremonger@intel.com>