net: xdp: remove unused bfp_warn_invalid_xdp_buffer()

net: xdp: remove unused bfp_warn_invalid_xdp_buffer()

After commit 8659fe126c808e5472664b2e1f0837844af4296b ("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 7faede04d6bf4508abe9e583fa89ba56cac94cfe.

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>