Remove the "betty" board configs from chromium.chromiumos.

We're not actually going to use that particular config.

R=jbudorick@chromium.org
BUG=732531

Change-Id: I6ab1cda23fdb621cccd19418263a57e955d032f8
Reviewed-on: https://chromium-review.googlesource.com/744594
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513034}

testing/buildbot/chromium.chromiumos.json

@@ -913,11 +913,6 @@
       "chromiumos_preflight"
     ]
   },
-  "chromeos-betty-rel": {
-    "additional_compile_targets": [
-      "chromiumos_preflight"
-    ]
-  },
   "chromeos-daisy-rel": {
     "additional_compile_targets": [
       "chromiumos_preflight"

tools/mb/mb_config.pyl

@@ -102,7 +102,6 @@
       'Linux ChromiumOS Full': 'chromeos_with_codecs_release_bot',
 
       'chromeos-amd64-generic-rel': 'cros_chrome_sdk',
-      'chromeos-betty-rel': 'cros_chrome_sdk',
       'chromeos-daisy-rel': 'cros_chrome_sdk',
       'linux-chromeos-rel': 'chromeos_with_codecs_release_bot',
       'linux-chromeos-dbg': 'chromeos_with_codecs_debug_bot',
@@ -576,7 +575,6 @@
 
     'tryserver.chromium.chromiumos': {
       'chromeos-amd64-generic-rel': 'cros_chrome_sdk',
-      'chromeos-betty-rel': 'cros_chrome_sdk',
       'chromeos-daisy-rel': 'cros_chrome_sdk',
       'linux-chromeos-rel': 'chromeos_with_codecs_release_trybot',
       'linux-chromeos-compile-dbg': 'chromeos_with_codecs_debug_bot',