remove unused ImageList member

since

commit 284ca1a584
Author: Noel Grandin <noelgrandin@gmail.com>
Date:   Sat May 28 14:38:03 2016 +0200

    Convert RSC_TOOLBOX to scoped enum

    and drop unused (in .src files) constants

Change-Id: I0e05389e1bbd5f74ff3b3cd9f1f16cfd54b992c2

include/vcl/toolbox.hxx

@@ -93,7 +93,6 @@ class VCL_DLLPUBLIC ToolBox : public DockingWindow
 private:
     ImplToolBoxPrivateData*   mpData;
     std::vector<ImplToolSize> maFloatSizes;
-    ImageList           maImageList;
     Idle               *mpIdle;
     Rectangle           maUpperRect;
     Rectangle           maLowerRect;