Revert "release: Ship firmware from kmods repo on DVD"

As we did in 14.4, this needs to be backed out of 15.1 to fix the
build. We're going to ship kmods built on 15.0 instead of 15.1 on
the DVD but hopefully those will work.

This reverts commit b0fbed20ceb9b899e7e20bf785e9d303608bc7a0.

Approved by: re (cperciva)