Remove JApplet check from SwingBuilder factory registration

`JApplet` has been deprecated for quite some time now (since Java 9) and was finally removed in Java 26. That means that SwingBuilder will stop working in Java 26:
```
Exception in thread "main" java.lang.RuntimeException: Could not init groovy.swing.SwingBuilder because of an exception in groovy.swing.SwingBuilder.registerBasicLayouts
	at groovy.util.FactoryBuilderSupport.callAutoRegisterMethods(FactoryBuilderSupport.java:211)
	at groovy.util.FactoryBuilderSupport.autoRegisterNodes(FactoryBuilderSupport.java:185)
	at groovy.util.FactoryBuilderSupport.<init>(FactoryBuilderSupport.java:163)
	at groovy.swing.SwingBuilder.<init>(SwingBuilder.groovy:101)
	at groovy.swing.SwingBuilder.<init>(SwingBuilder.groovy)
...
Caused by: java.lang.reflect.InvocationTargetException
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:119)
	at java.base/java.lang.reflect.Method.invoke(Method.java:565)
	at groovy.util.FactoryBuilderSupport.callAutoRegisterMethods(FactoryBuilderSupport.java:206)
	... 6 more
Caused by: java.lang.NoClassDefFoundError: javax/swing/JApplet
	at groovy.swing.SwingBuilder.registerBeanFactory(SwingBuilder.groovy:303)
	at groovy.util.FactoryBuilderSupport.registerBeanFactory(FactoryBuilderSupport.java:644)
	at groovy.swing.SwingBuilder.registerBasicLayouts(SwingBuilder.groovy:229)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
	... 8 more
Caused by: java.lang.ClassNotFoundException: javax.swing.JApplet
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:580)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:502)
	... 12 more
```

Author: jochenberger

subprojects/groovy-swing/src/main/groovy/groovy/swing/SwingBuilder.groovy

@@ -300,7 +300,6 @@ class SwingBuilder extends FactoryBuilderSupport {
         } else if (JTable.isAssignableFrom(klass)) {
             registerFactory(nodeName, groupName, new TableFactory(klass))
         } else if (JComponent.isAssignableFrom(klass)
-            || JApplet.isAssignableFrom(klass)
             || JDialog.isAssignableFrom(klass)
             || JFrame.isAssignableFrom(klass)
             || JWindow.isAssignableFrom(klass)