infra: Convert linux-chromeos-rel on the CQ to builderless.

crrev.com/i/3372943 allocates the machines, so this should wait for that
to land before proceeding.

Bug: 1140727
Change-Id: Id91cbeb7091fb9368dffc2d577bc9cf4873721af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2510434Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823199}

infra/config/generated/cr-buildbucket.cfg

@@ -28353,12 +28353,11 @@ buckets {
       name: "linux-chromeos-rel"
       swarming_host: "chromium-swarm.appspot.com"
       swarming_tags: "vpython:native-python-wrapper"
-      dimensions: "builderless:1"
+      dimensions: "builder:linux-chromeos-rel"
       dimensions: "cores:8"
       dimensions: "cpu:x86-64"
       dimensions: "os:Ubuntu-16.04"
       dimensions: "pool:luci.chromium.try"
-      dimensions: "ssd:0"
       exe {
         cipd_package: "infra/recipe_bundles/chromium.googlesource.com/chromium/tools/build"
         cipd_version: "refs/heads/master"

infra/config/subprojects/chromium/try.star

@@ -672,6 +672,7 @@ try_.chromium_chromiumos_builder(
 try_.chromium_chromiumos_builder(
     name = "linux-chromeos-rel",
     branch_selector = branches.ALL_BRANCHES,
+    builderless = not settings.is_master,
     goma_jobs = goma.jobs.J150,
     main_list_view = "try",
     tryjob = try_.job(),