[ci] Finish migrating Pigeon tests to LUCI (flutter#3192)

Completes the migration of macOS CI tests to LUCI, since the Pigeon test issues in CI seems to be resolved now (likely due to the Xcode updates in CI).

Fixes flutter#120231

Author: stuartmorgan-g

.cirrus.yml

@@ -22,13 +22,6 @@ tool_setup_template: &TOOL_SETUP_TEMPLATE
   tool_setup_script:
     - .ci/scripts/prepare_tool.sh
 
-macos_template: &MACOS_TEMPLATE
-  # Only one macOS task can run in parallel without credits, so use them for
-  # PRs on macOS.
-  use_compute_credits: $CIRRUS_USER_COLLABORATOR == 'true'
-  macos_instance:
-    image: ghcr.io/cirruslabs/macos-ventura-xcode:14.3
-
 flutter_upgrade_template: &FLUTTER_UPGRADE_TEMPLATE
   upgrade_flutter_script:
     # Channels that are part of our normal test matrix use a pinned,
@@ -335,24 +328,3 @@ task:
         - cd ../..
         - flutter packages get
         - dart testing/web_benchmarks_test.dart
-
-# macOS tasks.
-task:
-  << : *FLUTTER_UPGRADE_TEMPLATE
-  << : *MACOS_TEMPLATE
-  matrix:
-    - name: macos-custom_package_tests
-      env:
-        PATH: $PATH:/usr/local/bin
-        matrix:
-          CHANNEL: "master"
-          CHANNEL: "stable"
-      # Create an iPhone 13, to match what is available on LUCI, since Pigeon tests
-      # currently have a hard-coded device.
-      create_simulator_script:
-        - xcrun simctl list
-        - xcrun simctl create "iPhone 13" com.apple.CoreSimulator.SimDeviceType.iPhone-13 com.apple.CoreSimulator.SimRuntime.iOS-16-4
-      local_tests_script:
-        # script/configs/linux_only_custom_test.yaml
-        #   Custom tests need Chrome for these packages. (They run in linux-custom_package_tests)
-        - ./script/tool_runner.sh custom-test --exclude=script/configs/linux_only_custom_test.yaml

packages/pigeon/tool/run_tests.dart

@@ -119,10 +119,7 @@ Future<void> main(List<String> args) async {
     // androidJavaIntegrationTests,
     // androidKotlinIntegrationTests,
   ];
-  // Run macOS and iOS tests on macOS, since that's the only place they can run.
-  // TODO(stuartmorgan): Move everything to LUCI, and eliminate the LUCI/Cirrus
-  // separation. See https://github.com/flutter/flutter/issues/120231.
-  const List<String> macOSHostLuciTests = <String>[
+  const List<String> macOSHostTests = <String>[
     iOSObjCUnitTests,
     // TODO(stuartmorgan): Enable by default once CI issues are solved; see
     // https://github.com/flutter/packages/pull/2816.
@@ -132,8 +129,6 @@ Future<void> main(List<String> args) async {
     // should be enabled if any iOS-only tests are added (e.g., for a feature
     // not supported by macOS).
     // iOSSwiftIntegrationTests,
-  ];
-  const List<String> macOSHostCirrusTests = <String>[
     iOSSwiftUnitTests,
     macOSSwiftUnitTests,
     macOSSwiftIntegrationTests,
@@ -146,8 +141,7 @@ Future<void> main(List<String> args) async {
 
   _validateTestCoverage(<List<String>>[
     linuxHostTests,
-    macOSHostLuciTests,
-    macOSHostCirrusTests,
+    macOSHostTests,
     windowsHostTests,
     // Tests that are deliberately not included in CI:
     <String>[
@@ -177,11 +171,7 @@ Future<void> main(List<String> args) async {
 
   final List<String> testsToRun;
   if (Platform.isMacOS) {
-    if (Platform.environment['LUCI_CI'] != null) {
-      testsToRun = macOSHostLuciTests;
-    } else {
-      testsToRun = macOSHostCirrusTests;
-    }
+    testsToRun = macOSHostTests;
   } else if (Platform.isWindows) {
     testsToRun = windowsHostTests;
   } else if (Platform.isLinux) {