qemu-build: Simplify
qemu-build: Simplify

This reverts some of the changes to the script made to support features
other than what it was meant to do: build a docker image, and build qemu
in that image.

In it's current form it's failing to produce a qemu artifact for the CI
system to use. By simplifying it we have a better chance of debugging
the issue, and in fact the issue has gone away.

Change-Id: Ia757c1139e964b240ea4a54ecc7e24a5894e4cd9
Signed-off-by: Joel Stanley <4816dabf8db1bc6cac35b3a24cab2ff844b5b0c7@jms.id.au>

openbmc/openbmc-build-scripts,openbmc/openbmc-build-scripts