Fix wxDataViewCtrl::ClearColumns() crash on macOS 10.13

When replacing m_OutlineView with a new one in ClearColumns(), we must
explicitly remove the old one from its superview to ensure that no more
drawing operations are pending for it. Without this change, Cocoa
drawing code would occasionally crash on attempting to message the
now-zombie m_OutlineView instance. This happened in older macOS
versions too, but became much more frequent in 10.13 High Sierra.

src/osx/cocoa/dataview.mm

@@ -2089,6 +2089,8 @@ bool wxCocoaDataViewControl::ClearColumns()
     // columns cannot be deleted if there is an outline column in the view;
     // therefore, the whole view is deleted and newly constructed:
     RemoveAssociation(m_OutlineView); // undo InitOutlineView's association
+
+    [m_OutlineView removeFromSuperviewWithoutNeedingDisplay];
     [m_OutlineView release];
     m_OutlineView = [[wxCocoaOutlineView alloc] init];
     [((NSScrollView*) GetWXWidget()) setDocumentView:m_OutlineView];