Simplify JsonTypeInfo stub

Co-authored-by: Anders Schack-Mulligen <aschackmull@users.noreply.github.com>

Author: artem-smotrakov

java/ql/test/stubs/jackson-databind-2.10/com/fasterxml/jackson/annotation/JsonTypeInfo.java

@@ -14,14 +14,8 @@ public static enum Id {
         CLASS("@class"),
         MINIMAL_CLASS("@c");
 
-        private final String _defaultPropertyName;
+        private Id(String defProp) { }
 
-        private Id(String defProp) {
-            this._defaultPropertyName = defProp;
-        }
-
-        public String getDefaultPropertyName() {
-            return this._defaultPropertyName;
-        }
+        public String getDefaultPropertyName() { return null; }
     }
 }