This needs a waterfall configuration change to remove the build column (along with waterfall restart).

https://uberchromegw.corp.google.com/i/chromeos.chrome/waterfall

As well as a chromeos_config.py to remove the build configuration.

This can be done in either order, but the waterfall column will start failing very early if the build configuration is removed first.

CL to remove x86-alex from the waterfall is here:
https://chrome-internal-review.googlesource.com/c/392889/

Eliminating x86-alex from chromeos_config.py entirely would require modifying a lot of tests that use it as a test configuration. We have a number of other stale configurations there (e.g mario) so I don't see any reason to single out x86-alex here. The only place where it appears to need to be removed from chromite is for the SoM builders (https://chromium-review.googlesource.com/c/531632/).

The following revision refers to this bug:
  https://chrome-internal.googlesource.com/chrome/tools/build/+/aa66d91f411b91e1dcbf4370cba94cf54e2ff80e

commit aa66d91f411b91e1dcbf4370cba94cf54e2ff80e
Author: Steven Bennetts <stevenjb@chromium.org>
Date: Tue Jun 13 16:47:52 2017

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/chromite/+/c639f76022d60886762c946a6f7948e3663760e8

commit c639f76022d60886762c946a6f7948e3663760e8
Author: Steven Bennetts <stevenjb@chromium.org>
Date: Wed Jun 28 00:56:10 2017

Elim x86-alex-tot-chrome-pfq-informational from SoM

BUG= chromium:732460 
TEST=Builder should not show up in SoM

Change-Id: I3113a372ff3b29b1e7bb142518c4b60bee08c3e6
Reviewed-on: https://chromium-review.googlesource.com/531632
Commit-Ready: Steven Bennetts <stevenjb@chromium.org>
Tested-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>

[modify] https://crrev.com/c639f76022d60886762c946a6f7948e3663760e8/lib/constants.py