samples/bpf: Remove unused variable

The variable is never referenced in the code, just remove it
that this problem was discovered by reading code

Signed-off-by: Zhu Jun <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

samples/bpf/xdp2skb_meta_kern.c

···
 int _tc_mark(struct __sk_buff *ctx)
 {
 	void *data      = (void *)(unsigned long)ctx->data;
-	void *data_end  = (void *)(unsigned long)ctx->data_end;
 	void *data_meta = (void *)(unsigned long)ctx->data_meta;
 	struct meta_info *meta = data_meta;