Merge two wxDataViewWidgetImpl::Remove() overloads into one

Having 2 different overloads might have been useful for Carbon
implementation, but as they do exactly the same thing in the Cocoa
version, leave only one of them -- and don't pass it the item, or items,
being deleted as they're not used anyhow.

No real changes.

include/wx/osx/cocoa/dataview.h

@@ -486,10 +486,7 @@ public:
     virtual wxDataViewItem GetTopItem() const;
     virtual bool IsExpanded(const wxDataViewItem& item) const;
     virtual bool Reload();
-    virtual bool Remove(const wxDataViewItem& parent,
-                        const wxDataViewItem& item);
-    virtual bool Remove(const wxDataViewItem& parent,
-                        const wxDataViewItemArray& item);
+    virtual bool Remove(const wxDataViewItem& parent);
     virtual bool Update(const wxDataViewColumn* columnPtr);
     virtual bool Update(const wxDataViewItem& parent,
                         const wxDataViewItem& item);