Core: Do not use the obsolete (~20 years) ioctl /proc API.

The ioctl-based /proc API was obsoleted in Solaris 2.6 (July 1997),
but to be supported "until the next major release". In Solaris 11.4
(August 2018) the support has now finally been removed.

Most of the removed code was from 1995, and was thus older than Pike...