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 <zhujun2@cmss.chinamobile.com>
Link: https://lore.kernel.org/r/20241120032241.5657-1-zhujun2@cmss.chinamobile.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Zhu Jun

samples/bpf/xdp2skb_meta_kern.c

@@ -63,7 +63,6 @@ SEC("tc_mark")
 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;