Revert "Fix mac-sdk build & support darwin hosts (hopefully)"

There isn't any real reason to build darwin at all so we will just
disable it entirely.

This reverts commit eab990b981d3a9eea45f4afad8920b3d87c4b03d.

Reason for revert: Disabling darwin build seems a better long-term
solution.

Test: linux builds.

Change-Id: I2a113ca379c9aa4ca858fd6599275bd892d87d2e
4 files changed