bpf: remove unused parameter in __bpf_free_used_btfs

Fixes a compiler warning. The __bpf_free_used_btfs function
was taking an extra unused struct bpf_prog_aux *aux param

Signed-off-by: Rafael Passos <rafael@rcpassos.me>
Link: https://lore.kernel.org/r/20240615022641.210320-3-rafael@rcpassos.me


Signed-off-by: Alexei Starovoitov <ast@kernel.org>