linux-mini-orchestrator needs goma_backend

The mini-orchestrator recipe uses the build config of the compiler
builder passed in so chromium_tests assumes that the orchestrator
builder is going to compile too and checks if goma is there.
The chromium_tests module should probably be updated to accommodate this
use case, but for now this is a quick way to get it working.

Failing build: https://ci.chromium.org/ui/p/chromium/builders/try/linux-warmed-orchestrator/5/steps?succeeded=true&debug=false

Bug: 1149606
Change-Id: Idad26bf842ef094f0da160d53931c9928f949d9f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2586249Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Commit-Queue: Stephanie Kim <kimstephanie@google.com>
Cr-Commit-Position: refs/heads/master@{#835932}

infra/config/generated/cr-buildbucket.cfg

@@ -35174,7 +35174,7 @@ buckets {
         cipd_version: "refs/heads/master"
         cmd: "recipes"
       }
-      properties: "{\"$build/goma\":{\"use_luci_auth\":true},\"$kitchen\":{\"devshell\":true,\"git_auth\":true},\"$recipe_engine/isolated\":{\"server\":\"https://isolateserver.appspot.com\"},\"builder_group\":\"tryserver.chromium.linux\",\"builder_to_trigger\":{\"builder_group\":\"tryserver.chromium.linux\",\"buildername\":\"linux-warmed\"},\"recipe\":\"chromium/mini_orchestrator\"}"
+      properties: "{\"$build/goma\":{\"enable_ats\":true,\"rpc_extra_params\":\"?prod\",\"server_host\":\"goma.chromium.org\",\"use_luci_auth\":true},\"$kitchen\":{\"devshell\":true,\"git_auth\":true},\"$recipe_engine/isolated\":{\"server\":\"https://isolateserver.appspot.com\"},\"builder_group\":\"tryserver.chromium.linux\",\"builder_to_trigger\":{\"builder_group\":\"tryserver.chromium.linux\",\"buildername\":\"linux-warmed\"},\"recipe\":\"chromium/mini_orchestrator\"}"
       execution_timeout_secs: 14400
       expiration_secs: 7200
       caches {

infra/config/subprojects/chromium/try.star

@@ -1073,7 +1073,6 @@ try_.chromium_linux_builder(
 try_.chromium_linux_builder(
     name = "linux-warmed-orchestrator",
     executable = "recipe:chromium/mini_orchestrator",
-    goma_backend = None,
     properties = {
         "builder_to_trigger": {
             "builder_group": "tryserver.chromium.linux",