chromeos_config: Remove x86-generic-incremental

Removed x86-generic-incremental builder, and x86-generic-full from the waterfall
external list.

BUG=chromium:729645
TEST=chromeos_config_unittest

Change-Id: Id74134da73c8fe3b17c15e38e82c232df1fd0367
Reviewed-on: https://chromium-review.googlesource.com/666235
Commit-Ready: Paul Hobbs <phobbs@google.com>
Tested-by: Paul Hobbs <phobbs@google.com>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
3 files changed