[ci] Convert version presubmit check to LUCI (flutter#4822)

Adds a LUCI version of the version presubmit check, using the new label passthrough functionality, and removes it from Cirrus. Since that was the last Cirrus task, this removes the entire Cirrus config, and the associated Dockerfile.

Part of flutter/flutter#130076

.ci/scripts/check_version.sh

@@ -4,14 +4,13 @@
 # found in the LICENSE file.
 set -e
 
-# For pre-submit, this is currently run in Cirrus; see TODO below.
+# For pre-submit, check for missing or breaking changes that don't have a
+# corresponding override label.
 # For post-submit, ignore platform interface breaking version changes and
 # missing version/CHANGELOG detection since PR-level overrides aren't available
 # in post-submit.
 if [[ $LUCI_PR == "" ]]; then
   ./script/tool_runner.sh version-check --ignore-platform-interface-breaks
 else
-  # TODO(stuartmorgan): Migrate this check from Cirrus. See
-  # https://github.com/flutter/flutter/issues/130076
-  :
+  ./script/tool_runner.sh version-check --check-for-missing-changes --pr-labels="$PR_OVERRIDE_LABELS"
 fi

.ci/targets/repo_checks.yaml

@@ -44,13 +44,14 @@ tasks:
     script: script/tool_runner.sh
     args: ["dependabot-check"]
     always: true
-  - name: publishability
-    script: script/tool_runner.sh
-    args: ["publish-check", "--allow-pre-release"]
-    always: true
   - name: CHANGELOG and version validation
     script: .ci/scripts/check_version.sh
     always: true
   - name: federated safety check
     script: .ci/scripts/check_federated_safety.sh
     always: true
+  # This is the slowest test, so prefer keeping it last.
+  - name: publishability
+    script: script/tool_runner.sh
+    args: ["publish-check", "--allow-pre-release"]
+    always: true