doc: remove TUN from TAP PMD guide
doc: remove TUN from TAP PMD guide

TUN PMD is not supported, removing the references
from Network Interface Controller Driver Tun/Tap
Poll Mode Driver section

Signed-off-by: Vipin Varghese <b0b9508e3fd3e721e16f75bda9fcfd493661c711@intel.com>
Reviewed-by: Ferruh Yigit <ba8734c3c506d2e3557bd4ac8fdaccd25bdb9aa7@intel.com>

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