fou: Remove XRFM from NET_FOU Kconfig

fou: Remove XRFM from NET_FOU Kconfig

XRFM is no longer needed for configuring FOU tunnels
(CONFIG_NET_FOU_IP_TUNNELS), remove from Kconfig.

Also remove the xrfm.h dependency in fou.c. It was
added in '3045cb8aee2a ("fou: Support for foo-over-udp RX path")'
for depencies of udp_del_offload and udp_offloads, which were removed in
'e5ae3b9c947d ("fou: change to use UDP socket GRO")'.

Built and installed kernel and setup GUE/FOU tunnels.

Signed-off-by: Coco Li <lixiaoyan@google.com>
Link: https://lore.kernel.org/r/20220411213717.3688789-1-lixiaoyan@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>