Don't set m_manuallySetWidth incorrectly

This fix for disallowing shrinking the last column to nothing instead of
showing horizontal scrollbar when it became smaller than its minimum
size was wrong and is not necessary any more after the correct fix in
the previous commit.

This effectively reverts 0c90ea40c3 (Don't auto-resize wxDataViewCtrl
columns below their initial size, 2019-10-03).

See #18343.

include/wx/generic/dataview.h

@@ -137,15 +137,6 @@ public:
         if ( width == m_width )
             return;
 
-        // Normally we don't update it here as this method is called by
-        // UpdateColumnSizes() which resizes the column automatically, and not
-        // "manually", but if it's the first time the width is being set for a
-        // column created with the default width, do set m_manuallySetWidth in
-        // order to prevent the column from becoming narrower than its initial
-        // size when the control is resized, as this is unexpected.
-        if ( m_width == -1 )
-            m_manuallySetWidth = width;
-
         m_width = width;
         UpdateWidth();
     }