bpf: Remove __prog kfunc arg annotation

bpf: Remove __prog kfunc arg annotation

Now that all the __prog suffix users in the kernel tree migrated to
KF_IMPLICIT_ARGS, remove it from the verifier.

See prior discussion for context [1].

[1] https://lore.kernel.org/bpf/CAEf4BzbgPfRm9BX=TsZm-TsHFAHcwhPY4vTt=9OT-uhWqf8tqw@mail.gmail.com/

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Link: https://lore.kernel.org/r/20260120222638.3976562-13-ihor.solodrai@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>