Stop using wxCOMMON_CALLBACK_PROLOGUE macro in wxGTK callbacks

No real changes, just simplify the code and stop using a macro
unnecessarily when we can use a simple inline function instead.

include/wx/gtk/window.h

@@ -171,14 +171,9 @@ public:
     virtual GtkWidget* GetConnectWidget();
     void ConnectWidget( GtkWidget *widget );
 
-    // Called from several event handlers, if it returns true or false, the
-    // same value should be immediately returned by the handler without doing
-    // anything else. If it returns -1, the handler should continue as usual
-    int GTKCallbackCommonPrologue(struct _GdkEventAny *event) const;
 
-    // Simplified form of GTKCallbackCommonPrologue() which can be used from
-    // GTK callbacks without return value to check if the event should be
-    // ignored: if this returns true, the event shouldn't be handled
+    // Returns true if GTK callbacks are blocked due to a drag event being in
+    // progress.
     bool GTKShouldIgnoreEvent() const;