fix system_flag deprecation warnings

Passing cpu_topology or scheduler_bind_type to erlang:system_flag/2 results
in an error report warning that the argument is deprecated and is slated
for removal in erts-5.10/OTP-R16. Since we're already past that version and
no substitute approach has yet been decided for these features, keep the
deprecation warning but bump the removal version it mentions up to Erlang
18.