Revert "Catch up with the old sysctl API"

This reverts commit 0c8e757f2df4bc472ceea3530110d43e3854d060.
Revert "Revert "Use sysctl module instead of libc hacks""

This reverts commit f9ea3560a4b952532b7a08e09c6f60ba240da841.

Yes, revert the revert! The memory leak should have been resolved in the
latest version of devel/py-sysctl.