refactor: Remove unused DEFAULT_NODE_FOLDER constant

Author: Artur-

flow-server/src/main/java/com/vaadin/flow/server/Constants.java

@@ -145,11 +145,6 @@ public final class Constants implements Serializable {
      */
     public static final boolean DEFAULT_REQUIRE_HOME_NODE_EXECUTABLE = false;
 
-    /**
-     * The default value for {@link InitParameters#NODE_FOLDER}.
-     */
-    public static final String DEFAULT_NODE_FOLDER = null;
-
     /**
      * The name of the environment variable that controls whether server-side
      * usage statistics is enabled.