Remove the modified flag in the EditTableDialog

Remove the flag storing the mofification status in the edit table
dialog. It's only been used in one place and there it was not even
really needed - so why bothering updating and maintaining it?

src/MainWindow.cpp

@@ -627,9 +627,7 @@ void MainWindow::editTable()
 
     EditTableDialog dialog(this);
     dialog.setActiveTable(&db, tableToEdit);
-    dialog.exec();
-    //check modified status
-    if(dialog.modified)
+    if(dialog.exec())
     {
         populateStructure();
         resetBrowser();