Remove unused field

See gh-17562

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/UndertowReactiveWebServerFactory.java

@@ -19,11 +19,9 @@ package org.springframework.boot.web.embedded.undertow;
 import java.io.Closeable;
 import java.io.File;
 import java.io.IOException;
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.LinkedHashSet;
-import java.util.List;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
 
@@ -55,9 +53,6 @@ public class UndertowReactiveWebServerFactory extends AbstractReactiveWebServerF
 
 	private Set<UndertowBuilderCustomizer> builderCustomizers = new LinkedHashSet<>();
 
-	@Deprecated
-	private List<UndertowDeploymentInfoCustomizer> deploymentInfoCustomizers = new ArrayList<>();
-
 	private Integer bufferSize;
 
 	private Integer ioThreads;