eliminate PERL_STACK_OVERFLOW_CHECK

eliminate PERL_STACK_OVERFLOW_CHECK

This macro is defined as NOOP on all platforms except for MacOS classic,
where it was added as a hook to allow for OSes that have a small CPU
stack size. Since pp_entersub et al don't actually use the CPU stack,
this hook looks misconceived from the beginning. So remove all
uses of it in the core.