LibGUI: Get rid of Model::ColumnMetadata and always use auto-sizing

Auto-sizing of view columns is now enabled by default. This removes the
last remaining need for ColumnMetadata, so this patch gets rid of it.

DevTools/HackStudio/FindInFilesWidget.cpp

@@ -143,7 +143,6 @@ FindInFilesWidget::FindInFilesWidget()
     m_button->set_preferred_size(100, 0);
 
     m_result_view = add<GUI::TableView>();
-    m_result_view->set_size_columns_to_fit_content(true);
 
     m_result_view->on_activation = [](auto& index) {
         auto& match = *(const Match*)index.internal_data();