Remove support for Thymeleaf

Closes gh-28611

spring-boot-project/spring-boot-cli/samples/ui.groovy

@@ -1,33 +0,0 @@
-package app
-
-@Grab("thymeleaf-spring5")
-@Controller
-class Example {
-
-	@RequestMapping("/")
-	public String helloWorld(Map<String,Object> model) {
-		model.putAll([title: "My Page", date: new Date(), message: "Hello World"])
-		return "home"
-	}
-}
-
-@Configuration(proxyBeanMethods = false)
-@Log
-class MvcConfiguration extends WebMvcConfigurerAdapter {
-
-	@Override
-	void addInterceptors(InterceptorRegistry registry) {
-		log.info "Registering interceptor"
-		registry.addInterceptor(interceptor())
-	}
-
-	@Bean
-	HandlerInterceptor interceptor() {
-		log.info "Creating interceptor"
-		[
-			postHandle: { request, response, handler, mav ->
-				log.info "Intercepted: model=" + mav.model
-			}
-		] as HandlerInterceptorAdapter
-	}
-}