Ant support is split off to a plugin.

core/src/main/java/hudson/ClassicPluginStrategy.java

@@ -238,7 +238,8 @@ public class ClassicPluginStrategy implements PluginStrategy {
     private static final List<DetachedPlugin> DETACHED_LIST = Arrays.asList(
         new DetachedPlugin("maven-plugin","1.296","1.296"),
         new DetachedPlugin("subversion","1.310","1.0"),
-        new DetachedPlugin("cvs","1.340","0.1")
+        new DetachedPlugin("cvs","1.340","0.1"),
+        new DetachedPlugin("ant","1.431","1.0")
     );
 
     /**