Fix wxJoystickEvent documentation after the last commit

Remove left over part of the old sentence.

Also add a link to GetButtonChange() to GetButtonOrdinal()
documentation.

interface/wx/event.h

@@ -1742,19 +1742,19 @@ public:
         Returns the identifier of the button changing state.
 
         The return value is @code 1 << n @endcode where @c n is the index of the
-        button changing state.
+        button changing state, which can also be retrieved using GetButtonOrdinal().
 
         Note that for @c n equal to 1, 2, 3 or 4 there are predefined @c wxJOY_BUTTONn
         constants which can be used for more clarity, however these constants are not
         defined for the buttons beyond the first four.
-        and whose values were 1 << n. To support more than four buttons, the return value
-        is now defined as 1 << n.
     */
     int GetButtonChange() const;
 
     /**
         Returns the 0-indexed ordinal of the button changing state.
 
+        @see GetButtonChange()
+
         @since 3.1.2.
     */
     int GetButtonOrdinal() const;