bpf: Remove the unnecessary insn buffer comparison

The variable 'insn' is initialized to 'insn_buf' without being changed, only
some helper macros are defined, so the insn buffer comparison is unnecessary.
Just remove it. This missed removal back in 2377b81d ("bpf: split shared
bpf_tcp_sock and bpf_sock_ops implementation").

Signed-off-by: Haiyue Wang <haiyue.wang@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20230108151258.96570-1-haiyue.wang@intel.com