bpf: Remove special_kfunc_set from verifier

JIRA: https://issues.redhat.com/browse/RHEL-78203

commit d848bba
Author: Yonghong Song <[email protected]>
Date:   Fri May 23 13:53:21 2025 -0700

    bpf: Remove special_kfunc_set from verifier
    
    Currently, the verifier has both special_kfunc_set and special_kfunc_list.
    When adding a new kfunc usage to the verifier, it is often confusing
    about whether special_kfunc_set or special_kfunc_list or both should
    add that kfunc. For example, some kfuncs, e.g., bpf_dynptr_from_skb,
    bpf_dynptr_clone, bpf_wq_set_callback_impl, does not need to be
    in special_kfunc_set.
    
    To avoid potential future confusion, special_kfunc_set is deleted
    and btf_id_set_contains(&special_kfunc_set, ...) is removed.
    The code is refactored with a new func check_special_kfunc(),
    which contains all codes covered by original branch
      meta.btf == btf_vmlinux && btf_id_set_contains(&special_kfunc_set, meta.func_id)
    
    There is no functionality change.
    
    Signed-off-by: Yonghong Song <[email protected]>
    Link: https://lore.kernel.org/r/[email protected]
    Signed-off-by: Alexei Starovoitov <[email protected]>

Signed-off-by: Viktor Malik <[email protected]>

Author: viktormalik