fix for upcoming Pd-0.46 that has removed sched_tick() argument

in Pd-0.46, there is no more `sys_time` and `sched_tick()` has it's argument removed.
quoting Miller's commit message that removed `sys_time` and the `sched_tick()` arg: 
> there's only one "reasonable" value to use anyhow

I'm aware that Pd-0.46 is not yet released and that libpd comes with it's own bundled version of Pd.

see libpd/libpd#53 why i do as i do...