Revert "Use the layout.json file to actually build the FS's specified in it."

This reverts commit 2ec52e39a6e64f3975d977966e06f2e32259d979.

I'm fairly certain this broke our public bots:
https://uberchromegw.corp.google.com/i/chromiumos/builders/x86-generic%20full/builds/12255

Running ['/b/cbuild/src/scripts/sdk_lib/enter_chroot.sh', '--chroot', '/b/cbuild/chroot', '--cache_dir', '/b/cbuild/.cache', '--', 'PARALLEL_EMERGE_STATUS_FILE=/home/chrome-bot/trunk/chroot/tmp/tmpLgFpZ_', './build_image', '--board=x86-generic', '--replace', '--symlink=factory_shim', '--build_attempt=3', 'factory_install'] failed with exit code 1

Setting time filesystem last checked to Thu Nov 19 11:00:00 2009

mkfs.vfat 3.0.9 (31 Jan 2010)
Loop device does not match a floppy size, using default hd params
Cleaning up mounts
An error occurred in your build so your latest output directory is invalid.
Running in non-interactive mode so deleting output directory.
Deleted /mnt/host/source/src/build/images/x86-generic/R34-5125.0.2013_12_18_2332-a3

BUG=chromium:325495

Change-Id: I503452be67825aaffccb5cf2d5f9f654fe9ad09a
Reviewed-on: https://chromium-review.googlesource.com/180822
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
6 files changed