net: xdp: remove unused bfp_warn_invalid_xdp_buffer()

net: xdp: remove unused bfp_warn_invalid_xdp_buffer()

After commit 1de9530b1c8b26543651f81406d32ceb6b06ff4c ("virtio-net:
remove the warning before XDP linearizing"), there's no users for
bpf_warn_invalid_xdp_buffer(), so remove it. This is a revert for
commit a83076cc7fcfe0f10729dcb496fee5d08f026c26.

Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>