chore!: Remove feature flag for old license checker which is no longer available (#15190)

Author: Artur-

flow-plugins/flow-plugin-base/src/main/java/com/vaadin/flow/plugin/base/BuildFrontendUtil.java

@@ -365,8 +365,7 @@ public static void runFrontendBuild(PluginAdapterBase adapter)
             throws TimeoutException, URISyntaxException {
         FeatureFlags featureFlags = getFeatureFlags(adapter);
 
-        LicenseChecker.setStrictOffline(
-                !featureFlags.isEnabled(FeatureFlags.OLD_LICENSE_CHECKER));
+        LicenseChecker.setStrictOffline(true);
 
         FrontendToolsSettings settings = getFrontendToolsSettings(adapter);
         FrontendTools tools = new FrontendTools(settings);

flow-server/src/main/java/com/vaadin/experimental/FeatureFlags.java

@@ -64,9 +64,6 @@ public class FeatureFlags implements Serializable {
     public static final Feature HILLA_ENGINE = new Feature(
             "Multi-module engine in Hilla", "hillaEngine",
             "https://github.com/vaadin/flow/issues/9010", true, null);
-    public static final Feature OLD_LICENSE_CHECKER = new Feature(
-            "Old license checker", "oldLicenseChecker",
-            "https://github.com/vaadin/platform/issues/2984", false, null);
     public static final Feature COLLABORATION_ENGINE_BACKEND = new Feature(
             "Collaboration Engine backend for clustering support",
             "collaborationEngineBackend",
@@ -94,7 +91,6 @@ public FeatureFlags(Lookup lookup) {
         features.add(new Feature(EXAMPLE));
         features.add(new Feature(HILLA_PUSH));
         features.add(new Feature(HILLA_ENGINE));
-        features.add(new Feature(OLD_LICENSE_CHECKER));
         features.add(new Feature(COLLABORATION_ENGINE_BACKEND));
         features.add(new Feature(WEBPACK));
         features.add(new Feature(ENFORCE_FIELD_VALIDATION));

vaadin-dev-server/src/main/java/com/vaadin/base/devserver/startup/DevModeInitializer.java

@@ -205,8 +205,7 @@ public static DevModeHandler initDevModeHandler(Set<Class<?>> classes,
         // This needs to be set as there is no "current service" available in
         // this call
         FeatureFlags featureFlags = FeatureFlags.get(context);
-        LicenseChecker.setStrictOffline(
-                !featureFlags.isEnabled(FeatureFlags.OLD_LICENSE_CHECKER));
+        LicenseChecker.setStrictOffline(true);
 
         featureFlags.setPropertiesLocation(config.getJavaResourceFolder());