bpf: Remove unused btf_struct_access stub

This stub was not being used anywhere.
Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
Link: https://lore.kernel.org/r/590e7bd6172ffe0f3d7b51cd40e8ded941aaf7e8.1663683114.git.dxu@dxuuu.xyzSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

include/net/netfilter/nf_conntrack_bpf.h

@@ -3,8 +3,6 @@
 #ifndef _NF_CONNTRACK_BPF_H
 #define _NF_CONNTRACK_BPF_H
 
-#include <linux/bpf.h>
-#include <linux/btf.h>
 #include <linux/kconfig.h>
 #include <linux/mutex.h>
 
@@ -31,16 +29,6 @@ static inline void cleanup_nf_conntrack_bpf(void)
 {
 }
 
-static inline int nf_conntrack_btf_struct_access(struct bpf_verifier_log *log,
-						 const struct btf *btf,
-						 const struct btf_type *t, int off,
-						 int size, enum bpf_access_type atype,
-						 u32 *next_btf_id,
-						 enum bpf_type_flag *flag)
-{
-	return -EACCES;
-}
-
 #endif
 
 #endif /* _NF_CONNTRACK_BPF_H */