cmGeneratorTarget: Drop unused GetIDLSources method

Source/cmGeneratorTarget.cxx

@@ -547,12 +547,6 @@ void cmGeneratorTarget::GetModuleDefinitionSources(
   IMPLEMENT_VISIT(SourceKindModuleDefinition);
 }
 
-void cmGeneratorTarget::GetIDLSources(std::vector<cmSourceFile const*>& data,
-                                      const std::string& config) const
-{
-  IMPLEMENT_VISIT(SourceKindIDL);
-}
-
 void cmGeneratorTarget::GetHeaderSources(
   std::vector<cmSourceFile const*>& data, const std::string& config) const
 {

Source/cmGeneratorTarget.h

@@ -118,8 +118,6 @@ public:
                                   const std::string& config) const;
   void GetResxSources(std::vector<cmSourceFile const*>&,
                       const std::string& config) const;
-  void GetIDLSources(std::vector<cmSourceFile const*>&,
-                     const std::string& config) const;
   void GetExternalObjects(std::vector<cmSourceFile const*>&,
                           const std::string& config) const;
   void GetHeaderSources(std::vector<cmSourceFile const*>&,