Fix warning C4273: 'ToolbarValue::~ToolbarValue' : inconsistent dll linkage

That destructor is defined in vcl/source/gdi/outdevnative.cxx anyway.
(As empty there, too.) What is going on here?

Change-Id: Id27f07d47d819a4eaf272819a2e058f5f930b7be

sfx2/source/sidebar/TitleBar.cxx

@@ -23,8 +23,6 @@
 #include <vcl/gradient.hxx>
 #include <vcl/lineinfo.hxx>
 
-ToolbarValue::~ToolbarValue (void) {}
-
 namespace
 {
     const static sal_Int32 gnLeftIconSpace (3);