Remove support for the base/* toolchain ports.

These ports have been removed so these knobs are no longer meaningful.

This reverts commit 608289394f655d0635c71233248b734010fb4d2f.
This reverts commit 39eb07f172921a581ee9b33ca2765905f4235202.

Reviewed by: imp, bapt, emaste
Differential Revision: https://reviews.freebsd.org/D38562