8313403: Remove unused 'mask' field from JFormattedTextField

Reviewed-by: prr, honkar

Author: aivanov-jdk

src/java.desktop/share/classes/javax/swing/JFormattedTextField.java

@@ -288,10 +288,6 @@ public class JFormattedTextField extends JTextField {
      * Used to set the dirty state.
      */
     private DocumentListener documentListener;
-    /**
-     * Masked used to set the AbstractFormatterFactory.
-     */
-    private Object mask;
     /**
      * ActionMap that the TextFormatter Actions are added to.
      */