app/testpmd: fix CRC strip command

app/testpmd: fix CRC strip command

This patch fixed the bug that a failure appeared when config
rx_offload crc_strip using command "port config all crc-strip
on|off". The reason is that this command was removed in Commit
e5db17a1e54e. The current command is "port config <port_id>
rx_offload keep_crc on|off" instead.

In this patch, some codes left over about 'crc_strip' are
removed to make the current command clearer.

Fixes: e5db17a1e54e ("app/testpmd: remove duplicated Rx offload commands")
Cc: stable@dpdk.org
Signed-off-by: Ting Xu <ting.xu@intel.com>
Acked-by: Bernard Iremonger <bernard.iremonger@intel.com>